I can edit pictures for website development, I can use iTerm2 for programming in Vim and SSHing around to various boxes. I've been able to configure multiple local development environments including, but not limited to MySQL, PostgreSQL, PHP, nginx, Ruby, Django, and so on. Other various programs like my IRC client work splendidly and without issue.
The only thing that might make me switch back at this point is the direction OS X is heading in. I'm still on 10.6.8 and I refuse to upgrade until they make an OS that's faster and less buggy than the one I'm running. Lion and Mountain Lion don't fit that bill. Also, there's no backwards compatibility for Apps. More and more apps are becoming 10.7 only, which may force me to make a decision sooner than I'd like.
I mean it might seem to be like that at the beginning, only to find out later that some software just worked better on Linux.