I have been testing all of the software I can find for multimedia pcs, and here are some of the results of my finding.  To start out my overall findings are that none of these softwares are an integrated solution, and real HTPCs are still a generation out.  What we have right now are PC's with the ability to record, playback, and catalog media but that doesn't make it a true integrated media solution.  When I think of a HTPC I think of a PC that hooks only on to your TV and through a simple interfact with simple controls launches all the the media, programs, and games on your PC in a format that is easily viewable and managable on any TV.  With most of the software you can have your pick of two strong points, and two weaknesses.   For example you can have simple controls and a good TV interfact but you will not be able to launch games easily, or work with your programs.  I will start with Mythtv, a wonderful system, but it is exatly that system that renders it useless with your already existing system.  Freevo just doesn't have the features or smoothness required.  Geexbox is a fantastic program, however its stripped version of linux renders gaming or recording a non-possibility.  The Windows Media Center is a great example of almost there but it's lack of configurablilty renders it just another pretty interface.  MediaPortal is almost there as well, it just isn't quite configurable enough.  I also tried a game launcher called GameEx which seems to do the most, but it too is missing some really critical feature like voice commands and who wants to spent two weeks writting the commands for proper execution of games and emulator.  Overall we have one more revision before we get the REALLY cool media center PCs, however if I had to pick them It would be in this order:  MediaPortal for most overall ability and ease of use,  GameEx for most overall ability to configure all things you want to work.  Geexbox for fastbooting and easy media playback, and finally Mythtv as a Linux based solution (Really this is a toss up with Freevo which I like the interface and control better in, but MythTV take this for support, LiveCD, and stability).

So far the best overall home media solutions I have worked with are Xbox 360 coupled with TVersity Media Server software, and a modded original Xbox with Xbox Media Center.  Playstation 3 should be about the same with TVersity software as an Xbox 360 though I have yet to try.  The reason being that they are simple to use, play games, and playback multimedia file.  The drawbacks being that you cannot launch programs, or record TV with them without other hardware.  Overall though gaming consoles are the closest thing to where we all want to go.