My experience (6 PVR's since 1999) is that you can expect a PVR to last for 3 years, and anything else is gravy, or at least by that time it's very obsolete (and the hard drive becomes iffy) and you will want a new one anyway. In 3 years HD content will be common, also, pushing the obsolescence issue.
At $5 a month you can then add about $180 to that off-the-shelf price for the 510. More, if you expect to keep it longer than 3 years.
I would consider the new $299 721 offer...the 721's software is now mature and stable. It has a few minor issues, but to me its a true Tivo killer, and has no VOD fee. Name-based recording is only a few months away (they say).
