I have had two TiVos for about 2 years (maybe 3 - I've lost count) and they works great for SD content. I have older Series 1 TiVos and the limited Canadian support is not available for that so I have to stick to the roll your own data methodology. I use them with a SA3250HD and SA3200 terminals - I have minor issues of low volume levels on the SA3250HD. The TiVo uses an IR blaster to change channels on the STB and has to encode the video to MPEG-2.
Advantages of using a TiVo (vs. a SA PVR):
Much better UI, very few issues of missed shows.
Ability to export files to DVD.
Ability to export files to iPod and PSP.
Can schedule shows through a web interface.
Can use to play music, display photos.
Takes control of the tuner - you can't watch one show and record another.
Some of the above may require a bit of hacking.
Cost is about C$15 per month.
Can't do HD.