I initially installed myth on my main Ubuntu desktop as a DVD player to play a Region 2 DVD I picked up in Europe. But then I inherited a box from my brother that would do a good job. I found a decent rebate for a Hauppauge PVR-150 and I was hooked.
I ended up installing Unbuntu fiesty, and then adding the MythTV packages. Almost everything was pretty smooth. I signed up for zap2it (then swithced to Schedules Direct as that came online). A few shows start and end early, but I've out figured to start and stop recording a minute or two early or late. I've now seen most of my favorite series in syndication and my wife and I end up waiting for new episodes to come out.
The biggest problem I've had was with the remote control. I waited about 2 weeks before I had time to install it. I tried the default ubuntu package to no avail, and ended up compiling the packages from source. Everything worked fine for 6 months or so, but for some reason, the remote doesn't want to work now. I've tried reinstalling a couple of different packages, but to no avail. My next plan is to wait for the next Ubuntu release (8.04) and reinstall the whole box. That way I'll have 5 years of support with Ubuntus long term support release.
In the future I'm looking at getting an HDHomeRun, that I'll just be able to add to my network and capture 2 HD streams at once. I'd also like a second frontend for our living room tv.