The SageTV server hasn't been able to adjust recording times for those channels that start a minute earlier than expected. Yes, I know that this is more of a function of their scheduling service. The television schedule was part of the commercial package that I bought. It is much, much more inaccurate than the scheduling service (which I also paid much less for) for MythTV.
SageTV also loses to MythTV in the comparison of web interfaces for scheduling recordings of favorite shows. SageTV really doesn't have a "Favorites" feature unless you're willing to edit menu_items.js and then manually pick your shows. MythTV tracks your favorites, can automatically deconflict same-time recordings, and requires much fewer clicks to work around issues (if you need/want to take care of them manually).
SageTV has an interface to Squeezebox that will only play locally on the server. MythTV's interface (Slimp3) actually plays remotely, through the MVP box.
For remote access, you still need a client program for SageTV. For MythTV, the standard media players (Windows or Linux) will work via the web interface.
The extra features that SageTV does have (the ability to play directly off of GoogleVideo or YouTube, a handful of useful plugins, etc.), I can live without.
MythTV's shortcomings are minor. It isn't as hackable as SageTV (yes, the commercial product was easier to work with) and the community is a bit more friendly (I got a lot of abuse from the Myth developers for attempting to code something different from _their_ way. They actually were a bit proprietary about the code (they were angry that I was rewriting their code to do something they deemed useless)). You'd think that it'd be the other way around.
I stuck with SageTV for a very long time (through 2 versions), well past the point where MythTV was a better choice for me. I think this was caused by the manual configuration requirements needed for MythTV. (I could just never find the time to play with it.)
In any case, for those of you in the VPN (mostly those living in the house), the Sage interface is being taken down. The old rules of use for Sage now apply to Myth. For everybody else, notes in the wiki have been updated here and here.