Another huge Tivo HD fan here. We just upgraded from a Tivo Series 2 a couple of months ago, and love it. One nice thing is that by using a Cablecard, which is what you have to use with the Tivo HD, we don't have to use the cable company's box anymore. Comcast screwed up the install of the Cablecard on the first attempt, but everything has been fine since their second visit.
One other thing about fast-forwarding through commercials: you may have to do that on a cable company's DVR, but I never do that on my Tivo because I've programmed my remote with a 30-second skip feature. This website tells you how to do it:
http://bigmarv.net/how/tivo30secondskip.html
That feature, combined with the button that rewinds by 8 seconds, makes me get through shows so much faster. For example, I will NEVER watch Lost again if it's not on my Tivo, it's so much better to get through 3 minutes of commercials in 10 seconds.
We have to pay more per month for Tivo HD as compared to the cable company's DVR, but the increased features and ease of use of the Tivo software makes it worth it.