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.
I've been using ProjectM for some time now. In fact, it doesn't feel right listening to music without it running. Originally this project was limited to being a plugin for XMMS, beep-media-player & other music players.
Now projectM has a QT GUI which allows you to run it regardless of what media player you use. You can plug it into jack and listen to whichever audio output you want.
The most important feature added to projectM recently is a list of all the presets available to you; so you can jam along without having to skip annoying visuals.
I haven't tried the latest version as I'm using a old version of ubuntu.
Overall, projectM provides the most responsive visuals to music that I have seen. This new version has had some speedups too!
This software is prone to displaying flashing visuals which most epileptics will find to cause seizures.
I introduced my film loving friend to celtx recently. I hadn't read the feature list but I was sure it would provide some of the ones he wanted.
Within ten minutes he replied with a barrage of thanks. It appears that Celtx provided him with more power to do what he wanted than $400 applications could!
This friend is now happily utilizing celtx for his projects.