I've enjoyed using it for the last three years. It has quite a few features that the other DVR software packages don't. Plus an active support community. Plus being user-extensible.
The problem is that the version that I've purchased is starting to have some serious issues, mostly by not playing well with various upgrades to my system. Having to maintain two versions of Java (the older one for SageTV) and a number of legacy libraries was a serious P.I.T.A. On top of that, the online sources never really worked all that well (which can be blamed mostly on the serious shortage of documentation for the Linux version).
In any case, I'm considering moving away from SageTV. I really don't want to purchase the newest version. MythTV appears to have most of the features that I want and I'm willing to invest a few hours to get it up and running. I'll keep you posted.