@Vinod, there was little sarcasm in my post. I was being very forthright about what I think about the statements you made, as many of them are wrong, and you do the community a disservice by spreading FUD.
2. Again, you are just wrong here as well. When used incorrectly, like say putting the wrong aria tags in the wrong places, it can confuse screen readers, yes. That's like saying a hammer is bad because I can break windows with it. The question is, does Bootstrap misuse aria tags? And the answer is no they don't. They are additive semantic information, and bootstrap uses them correctly.
Your comments on data-* attributes seem misguided as well, as you seem to believe that browsers must support the HTML5 data spec or something along those lines for them to be useful, and that is not the case.
I'm wondering if you are running a site with bootstrap through some HTML style checker somewhere and it spit out warnings about these things or something and you took that as gospel? Because everything you said in this point was misleading.
3. Sure you did:
Bootstrap uses several nonsupported HTML attributes such as placeholder, required,aria attributes group, data attributes group & so on.
It uses data-attributes for local title storage which IE9+ (Yes IE 10 too!) do not support & yet again, no fallback!
Both of these statements belie some sort of misunderstanding as to what the data-* attributes are actually there for. But I digress. I agree that the tooltip is broken in older IEs, and that needs fixed at some point.
4. Oh, I'll agree that a FRAMEWORK should use !important VERY judiciously, but it is not an evil directive or something. It's purpose is for local override of cascading styles as needed. There is nothing evil about them, they are just a code smell (code smells are not in themselves evil, they are just warning signs). The important part (pun unintended) is that you use !important in only the right ways. Again, hammer, window, that sort of thing. Does Bootstrap do that?
I'll concede that it would be better if Bootstrap didn't use them AT ALL, but lets take a look at the places that bootstrap DOES use them:
1. Print styles - This should be pretty obvious why they use them here. This might be valid if you are worried about print styles that much, but the argument here should be "Bootstrap makes decisions about what a print style should look like that I might not like".
2. Utility responsive classes (.visible-phone, etc.) - Again, pretty obvious why here, as they are literally all utility classes meant to override default behavior. You don't ever have to use these.
3. .nav-collapse.collapse override for 768 max style sheet - This is the ONLY rule that uses it as a hack to achieve something in the ENTIRE framework. The only one.
5. I wish that were true actually, but it isn't. LESS is better supported as a toolset for the VisualStudio crowd, while finding a SASS solution that you can build into your build solution is much more difficult and requires a lot more tools to be available (e.g. Ruby, Gems, etc.). I actually like SASS better, but it fits much more with the Linux crowd than the Windows crowd right now. There ARE solutions for it, but not as easily integrated as the LESS ones...
In fact, both LESS and SASS made decisions about their development that makes them (and I mean the real distributions of them, not third party interpreters) reliant on an external tool chain. SASS with Ruby, and LESS with Node, which were both kind of short sighted and makes integrating with non-*nix based development environments much more difficult.
But that is kind of irrelevant to a discussion about Bootstrap, and more relevant to how Bootstrap works with Sitefinity, as it is a .NET application so Windows based development is the norm. So talking about it HERE means that LESS is actually the preferable method. But again, I wouldn't worry too much about that argument, as its more religious than substantive.
As I said at the beginning of my post, the question of limitations arises due to the nature of using a framework that forces choices on you.
My point was the conclusions you came to are based on faulty reasoning. I have no idea what your background happens to be, but you appear to be misinformed on a good deal here, and spreading that misinformation is going to confuse a lot of people who don't know better. Now if you want some ACTUAL short comings:
1. Bootstrap makes a lot of legitimate style choices (font sizes, colors, etc.) in the interest of typography that sometimes I wish they didn't... but you can override that in the LESS file, and really, you should be compiling a custom stylesheet when using bootstrap anyway. Some of that actually is supposed to go away in the next version, where they are going to a very flat style to allow for easier customization by people who don't compile though.
2. The print styles are actually kind of annoying sometimes. We've had to override them because they actually add the full URL of a link in parentheses after the link text when printing, but the rest isn't so bad.
3. Tooltip being broken I can't confirm right now. It is certainly broken on their site in IE8, but that may be due to the other JS error I'm getting on their page which is related to some image placeholder JS they have on there. I don't have any tooltips on my own site to try it.
4. Bootstrap is REALLY meant to be used as a base for site CSS, not out of the box, but a lot of people do, and I can't fault them for that. Bootstrap provides a lot of OOTB functionality and styles that I wish it didn't, but that can all be customized with LESS.
5. If you DO go the LESS route, you are likely to modify some of the source LESS files in the process. This makes upgrades a fun little nightmare as you have to reapply your changes manually usually. There are tricks to get around this, but none of it is fun. They try and make it easier with a settings LESS file, but often I find myself modifying other LESS files to get certain functionality (or to remove some, like the aforementioned print style). However, this is also a strength, because I CAN do this much more easily than modifying a monolithic CSS file every time they release.
6. I'd actually prefer some of the "features" to be better broken up in the LESS structure. There's a lot of components jammed together with default styles in several places that makes modification a bit harder than it should be. e.g. every single one called out in the components section should be its own LESS file. They seem to have actually started down this route though, so I can't really complain much now... it used to be a bigger issue. But for instance, why the hell isn't there a print.less file? Why is that globbed into reset.less?
7. Some components are almost useless unless you want to use them wholesale without much modification. Looking at you, navbar.
A lot of these come down to Bootstrap taking over more than I might want it to as a framework. Again, that's just a limitation of using a framework that makes choices for you.
Sorry if you took offense, but the guy who posted the link asked for discussion on the points you brought up, and its hard enough having reasoned discussion on valid points, let alone one based on faulty understanding. I stand by my assertion that most of your points are bull, for that reason.