Programmer Hubris - I don't run your software all the time.
Not only don't I run your software all the time, but actually I run it about once every couple of weeks.
So why on earth does your software run all the time?
Okay, so this particular complaint is about Sun's Java, which I use once every two weeks, to sign my timesheet so that I can get paid. It stays memory resident even after I close the web browser that took me to the page. But the complaint could equally well be made against RealPlayer (or whatever it's called this week), which likes to remain in my system tray (down by the clock) even though I view .RAM files about once every two or three months.
Maybe Java and RealPlayer occupy very small amounts of memory, but when you combine them with every other program whose developers assumed that everyone would be using their software 24x7, you wind up with a lot of memory used by a lot of programs that are all plodding along unused, but stealing a little time here, a little network resource there, and a bucket of memory.
Every now and again, I rebel, and remove a bunch of applications that I rarely use. But then, "rarely" comes around and I have to reinstall because there's a persentation I want to hear in RealPlayer, or an algorithm demonstration in Java. Then I have to uninstall again (and reboot) if I don't want to waste my resources.