MythTV is a Linux-based media centre program, but it also gives you so much more than that. I have to say that this is better than any other media centre software out there. Why is this?
It has been designed from the outset to provide a client/server architecture. This probably doesn't mean much to many people at the moment, but it is certainly the way forward. What you have is a back-end that provides the media content, then you have front-ends that allow you to access that content.
The simplest install is to have the back-end and front-end on the same computer, providing the same functionality as any other media system. If you plan to have more than one front-end you have have the back-end on another computer, but both will be able to access it. The back-end is also responsible for recording the TV and cataloguing the data, so you can stick a few TV cards in there and make simultaneous viewing and recordings. And for your front-end you can make it as powerful or lightweight and silent as you want as you can limit the moving parts when the brute force (apart from decoding) is provided by the server.
The real power comes from the client/server architecture, as the front-ends can be implemented in anything that you can connect to the MythTV protocol. This is most apparent because it easily has a front-end for web access (meaning you can schedule your recordings remotely), there are also other smaller front-ends to the default and even a small one for Windows which is functional. The back-end server software is pretty much rock solid because it builds on the foundations of Apache and MySQL.
Recently version 0.20 was released with a whole raft of new functionality including OpenGL UI rendering and a more library based architecture. You can see the rather long changelog here.
If you want to try this out you can also do this without installing it thanks to the wonders of KnoppMyth. This is a Knoppix based distribution on a CD/DVD with MythTV set up so you can try it out and if you like it install it.
There is also MythDora a Fedora-based MythTV distribution. This is based on Fedora Core 4, a little out of date.
There is an excellent resource for getting MythTV installed for Fedora here. This is highly recommended and comprehensive.
Also, for the Ubuntu people out there, you can use this resource to get the information you need.
Lets not forget the excellent documentation and the Wiki. You can see some themes here and some screenshots here. Also there are thriving communities including the forums and mailing lists at MythTV itself and KnoppMyth, and there is also MythTV Talk.
And here is a screenshot for the curious: