I use (Comcast supplied) Motorola Cable Box DVR, Series 2 Tivo, and have used both (free/open source) MythTV and ($) Snapstream's Beyond TV. While I like the free and open source nature of Myth, I must admit it was no small undertaking to build the machine. It was one of my first Linux experiences so everything came with a significant learning curve. After running with MythTV for several months, I ended up reverting back to Snapstream. But when the machine crashed, I just decided for rock-solid stability, Tivo and Motorola DVR beat software based solutions. I think this is due to the fact that a set-top box like the Tivo or Moto have custom configured hardware/firmware. With a computer, the software has to accomodate a wide variety of CPUs, OS versions, video capture cards, etc. The biggest feature I miss from the software based solutions is the commercial detection and auto-skipping....while not always perfect, it was a lot better than FF. Should anyone have any questions about my MythTV experience, let me know. Also, if you are going to venture into MythTV and are new to Linux, you might consider one of the LiveCD options like KnoppMyth which make installation and configuration of Myth as trivial as possible http://www.mysettopbox.tv/knoppmyth.html
Edit: I should also add that I stuck with the Comcast primarily due to the fact that it is the only solution (aside from buying a new Tivo series 3) that allows me to record Cable Hi Def. And it will record two shows at one. It requires no tinkering and rarely suffers from performance problems. Also, it cost $10/month for the box and the TV Guide service is built in for free (unlike Tivo). If the box fails (because they do get very hot in my AV cabinet), I can just call comcast and they replace it free.