Right now the current performance of inspections is limiting their usefulness. It takes too much time to reparse a file and if I am editing it constantly I completely loose the benefit of a smart editor catching my errors at the same time I do them (I loose my computer pair for the Pair-Programming crowd ;-).
Here are my thoughts and please feel free to shoot them down. I will file requests if people like them (and even if people don't like them anyway ;)
Have an incremental parsing/reporting: parse for compilation errors then for the custom error level then for the warning level (the builtin ones first then the third party later or have a configurable order). At any point if an inspection/syntax check returns a result report it immediately. As compilation errors are the most important they should have higher priority and run more often.
Use a junit metaphor for reporting progress and errors: Green/yellow/red bar progressively going to 100% when the file is fully parsed. Intentions can be viewed as tests. They give feedback and as usual the earlier the feedback the better.