I've been using Boxee for the past couple of days, and I'm pretty satisfied with it.
Hmm, I'll try and install it too. Tell me, does it alter your files in any way? Add hidden covers in your folders? Also, I found you in program so I'm "following" you now. 
Ah, I was wondering who added me on there.
I don't believe it modifies files in any way. I'm not sure about covers, as I'm back home for the break, so I won't be seeing my media center again until January.
There are a lot of cool plugins/apps that you can install for it, too, that allow you to do things like watch Hulu inside of it. Interestingly enough, it runs smoother in Boxee than in a browser, and I
think that Boxee was automatically muting the ads.