I was about to make one, but time warner cable offered one that had everything I needed for about $9 a month. It used the same browser as my old cable box. Stupid microsoft and their TiVO big brother monitoring crap.
The only problem with it is that I can't extract the video from the box, but with 50 hrs of data, it really hasn't been too big of a problem.
I don't want anyone knowing that I usually only watch Sci-Fi, Discovery channel, and TechTV for the most part. Well there's come Comedy Central, Speed, Spike, and a few others one the weekends. So I would prefer to build a DVR not buy one. Just in case those companies are not as trust worthy as you'd like them to be.