Personally, I went for SageTV. I set up my HTPC config about 3 years ago and at the time I found the alternatives lacking. MS Media Center was expensive, buggy and hard to get. Myth required Linux and a lot of hands on tweaking/configging which I didn't have time for (not to mention I am no Linux guru!) and Beyond at that time (IIRC) didn't have a good way to interface with a Dish Network receiver.

I first got SageTV version 2.1 (IIRC). I ran that up until this May when I did the free upgrade to version 5.0. It ran great up until and since then! I am running on a relatively modest box (AthXP 2500+ 512MB, Hauppauge 250 card, Radeon 9600XT, 300GB HD, Win2K Pro). This setup works great.

While the software isn't as open as Myth, it does have some facilities for writing plugins. The 5.0 version comes with a feature for pulling up local weather for instance. 

 5.0 added placeshifting capability ( being able, with their client licenses) to directly run a Hauppauge Media MVP unit (I have 2 of these) and/or PC Placeshifter client. With each of these, you get the full SageTV UI and can view both live and recorded content, set up recordings, etc. I have used the PC Placeshifter client on my laptop to watch TV while sitting in a hotel while on a business trip (because hotel cable usually sucks!) and I use the MVP units in the house to access my HTPC content in my family room and livingroom (the HTPC is in the bedroom).

 5.0 also added support for HiDef, but I don't have a HD card so I haven't tested that out yet.

 All in all, I'm VERY happy with Sage and can't see myself changing to anything else in the near future.

 --cbr600f4i