I still got debugging problems on OS X (SCR 28414). The main window simply disappears during debugging (expanding the this node in the debugger seems to be one thing that can trigger this problem).
Back then, when I submitted this bug I thought that this would be a Stopship bug for 4.0. Especially, as Maxim confirmed that he experienced this at least once. But when I checked the tracker just a few minutes ago, it wasn't even opened yet.
I have been a long time member of the EAP community, but this is not the IntelliJ I remember from the past good old days. Please decide whether you want to support OS X or not. I can accept that screen menu bar does not work (although I can't see any reasons why it works in other applications but not in IDEA) but I cannot accept that I cannot debug my programs.
I also submitted a bug for junit that didn't work as expected. The bug was closed as not repeatable. After that I took the time to recreate my project with dummy files to keep the original structure and attached it to the bug report. Never heard of it again. Maybe the error was in my code, it couldn't be reproduced or the person responsible didn't bother to reevaluate. Probably, I'l never know. Again, this is not the IntelliJ that I remeber from the good old days.
There's some files that slow IDEA down, that much that I can type faster than IDEA can keep up with my typing speed (it doesn't loose characters but it feels like working on a slow terminal). And no, I am not talking about files with 30k lines. I have complained about that since I don't remember when. Things got better but it is still far from perfect.
I am quite sure that I could come up with some more examples if I tried real hard. I am a student and have to decide carefully on what to spend my money on. I just bought an update to 4.0 but right now, I am close to reevaluating other IDEs. Eclipse doesn't meet the high editing standards that I am used to (yet?) but maybe it allows me to enter my code at full typing speed and debug my programs. Maybe it even has a community that I used to know from good old IDEA days. Even if not: it's for free.