I am keen to understand what are the real time challenges people are facing with their Legacy Applications
Hope this helps. These are off the top of my head.
1) Look and Feel - Our application is very 90's in the way it looks and feels, but it was developed with business logic and GUI in the same programs so is very hard to modernise without the use of services such as ConsultingWerk.
2) Use of shared variables throughout
3) The use of includes with compile time parameters
4) Legacy code that nobody really knows its purpose, but it's desperately inefficient. Not enough hours in the day to rework.
5) Bad design decisions (although they were possibly the only method at design time) that mean the complexity of modules is huge, but rewrite is expensive and risky.
6) Different methods and practises from a vast range of developers over the years making maintenance hard.