I'm looking for any good material on upgrading legacy systems from both an engineering and product management point of view. War stories are also welcome since they're fun to hear. Thanks for any help!
And finally, at the code level, it's absolutely essential to have a copy of Martin Fowler's Refactoring: Improving the Design of Existing Code handy. Yes, many tools have automated the mechanics of refactoring, but knowing when and how to use them needs this book.