Yes, SageTV has it's problems (just check their forums) but when I was evaluating media center servers + front ends, it offered the best feature set and ease of use. I love the fact that you can buy client boxes (like the MVP or the HD one) that entail no maintenance, are silent, and use less electricity.
There are a lot of things in SageTV that point to the fact that it was originally developed by developers for developers. The default interface is butt ugly and not very user friendly. If it wasn't for the SageMC interface that some guy developed, I would not have purchased Sage. Many people still have to make a registry change to increase their Java heap size. Lots of people do report problems with their setups though. However, the software is now present on Mac, Linux, and Windows, which is great.
Also, the company is not very communicative. There is one "community liaison" type who frequents the forum, but he often gives snarky or non-helpful answers. There is a core of long-time users who answer lots of people's questions and in a sense throw their weight around. It's a lot like the typical open source community... :)
If you want to, you can tweak the hell out of the software and install all sorts of stuff (like a NetFlix watch it now viewer, etc). Most of the tweaking can be done via a remote control through the client box. However, the architecture for plugins makes them difficult to install and get working. They also offer a software client that you can use from a PC.
I don't like the fact that they have an obfuscated database format.
Overall though, I've been very happy with SageTV. It was easy to set up and get working and I've had no major problems. Plus, the transition from Tivo was pretty easy in terms of the user interface.
Todd