In the amount of time not spent beating my head against the wall.
I'm in management these days, so I only have to deal with it as it impacts my schedules and retention. Upgrading My Eclipse Blue was incredibly painful. I get complaints about memory management, crashes, and EARs missing files. The integrated SVN system makes me weep when I have to try to explain to devs what /move and /switch SVN commands are. Or the inane restrictions our support team puts on our use of the product because they're trying to steer us around issues that will corrupt workspaces and configurations to which their only solution is uninstall/reinstall.
Same crap with XCode. We use to have a daily pool to see who could pull off the longest up time.
Now, if you want to get into code, things get a bit mirkier. Java is catching back up, but the .Net framework's implementation of generics and more importantly LINQ is still leaps and bounds over Java. And while Spring and other libraries have improved the ease and speed of data access over Hibernate, .Net's Entity Framework is super easy to work with (so long as there are good drivers for the DB you're hitting).
Java's documentation is superior, no questions there. Microsoft's MSDN isn't bad, but if I run into something odd, it's almost always augmented by Stack Overflow.
And historically speaking, I've had less issues upgrading the .Net framework on servers/desktops than changing Java version. Especially since .Net 3.0 (1->1.1->2.0 was rockier than I would have liked).
Anyway, they are all 3 valid development platforms. I have my preference, others have their own.
-Rick