I've read lots of good stuff about Paint.net too, but every time I've tried it, I end up back to use FireWorks and Photoshop.
I don't know, something about they way paint.net works, or it's ui, something, just kinda bugs me, but I've never really been able to put a finger on it.
But hey, if it works for you, go for it! It does seem to have a lot of capability. and the price is right!