Just the move to Unicode (i.e. from 2007 to 2009) took some work, but otherwise I can't think of any intentional breaking changes...? In fact, it's one of the most stable programming environments I know of – granted, in part because of being a little stagnant (but not dead).
I've been using Delphi since Delphi 3. The only really breaking change I can recall was the Unicode switch. And that was just a minor blip really. Our 300kloc project at work took a couple of days to clean up the compiler errors and it's been Unicode-handling ever since. It's file integration and database heavy, so lots of string manipulation.
Most of my hobby projects didn't need any code changes.
In fact, the reason Delphi was late to the Unicode party was precisely because they spent so much time designing it to minimize impact on legacy code.
Not saying there hasn't been some cases, but the developers of Delphi have had a lot of focus on keeping existing code running fine. We have a fair bit of code in production that is decades old, some before y2k, and it just keeps on ticking without modification as we upgrade Delphi to newer versions.
The market has been ignoring Delphi for that long. It probably peaked with D5, once they changed their name from Borland to Inprise, it was over.
I hear it's still somewhat popular in Eastern European countries, but I heard that several years ago.