Add me to the list of Cable/DVR owners (renters). The cost of a decent DVD recorder is still a couple hundred bucks at least, and it doesn't do HDTV. In a few years, maybe they will have HD recorders that work as well as the built in unit on my cable box... Even then, it's hard to beat a 10 buck a month rental fee and the reality that I can simply trade up for something better as it comes along, and never have to worry about it breaking and me being stuck with an out-of-warranty product.
Downside? Well, it only works on the TV I have it connected to... but I actually have it on 3 TVs so it isn't that big of a bummer. So, I can't take it to a friends house and watch a tape/DVD. Not once has that been an issue.