This is a great tool to free oneself from Windows. I have personally used it for running a game I was reimplementing so that I didn't have to jump between two PCs. It can save you if someone at work sends you something that can only be read on Windows. It's simply doing the dirty job. Even though we should ultimately aim for native Linux programs, Wine makes it less painful to exist in this world.
I use wine to run most of my windows games which aren't available for linux. Prey, Half-Life 1/2, Grand Theft Auto (3/VC/SA), Portal, Far Cry and many more run perfectly.
Most of the games that I have tend to run slowly when I had XP installed (for some reason). Amazingly, wine runs most of my games better than they did on XP!
I also use wine to allow my windows using friends to run their applications. I once had MS Office 2003 start up so fast on wine that me and my friend fell off our chairs! There was no way that XP started Office that fast.
Wine has become easier to use as of late, and you'll notice by the stats that development has been incredibly fast.
A small annoyance with this fast development is that certain games may become slow if you upgrade; this is because they are rewriting the pixel shaders. Eventually this will all calm down.