The IDE has had to be re-written for 32bit code.
Technically it's the libraries that have to be rewritten, although we do tend to use the term IDE to mean the lot around here.
I'm currently having a stab at porting to an LPC so I can appreciate the problems 
I suspect that some things just won't port across, but also there's the opportunity to add new features that weren't really practical with the smaller AVRs.
Rob