I didn't have much trouble getting it to work. So far it's been working fairly well; I'd say much better then it did on Jaunty. Here are the steps I did to install Boxee on karmic.
Add the Jaunty Repo as per the instructions
Install libdirectfb-1.0-0 -
https://launchpad.net/ubuntu/karmic/....0.1-11ubuntu1
Install liblzo1 -
https://launchpad.net/ubuntu/karmic/i386/liblzo1/1.08-3
Install libkrb53
https://launchpad.net/ubuntu/karmic/...beta1-5ubuntu2
Install boxee (apt-get install boxee)
Boxee has replaced mythtv as my default media center now that it isn't crashing nearly as much. Now, if only there was a mythtv plugin so it can automatically integrate my recorded TV recordings with the correct titles.
Bests,
-Hans