A bit late I realize, but I'm currently listening to Gieseking's WTC, Book 1. I was catching up on this thread and saw it mentioned, and then remembered that I had found a copy at my library last year and ripped it to MP3 along with a bunch of other stuff.
Overall this is better than I was expecting -- after one spin it's not breaking in among my favorites by any stretch, but I'm glad I've finally given it a listen. It has lousy sound quality (most likely due to excessive noise reduction, as I think George mentioned), and his speeds are a bit fast for me at times, although not universally so (I'm hearing BWV 849 now, and it's rather leisurely).
By the by, there also seems to be another Gieseking WTC out now, recorded for Saar Radio according to Amazon...