I was into IPSC in a big way when I lived in the UK. After the ban, I moved to the US... and have been working so hard I never get to shoot :-(
I like shooting USPSA matches; you get to blast off lots of rounds, and the standard of competition is impressive. However, USPSA is, IMHO, a much less disciplined sport... compared with non-US IPSC, the USPSA matches are very self-indulgent, sacrificing any vestiges of practicality in favor of "feel good" run-n-gun courses of fire. Not necesarily a bad thing, but a difference that I miss in comparison with European-style courses of fire.
IDPA is just another game (albeit a fun one). For all the talk about tactics/practicality, you have to just laugh when the big matches are won with 9mm 1911s... who are they trying to kid ? Their rule book is growing as fast as IPSC/USPSA.