I was curious if anyone has developed any custom front-end software for the Scientific atlanta 8300HD. Figured the 8300HD would make a great HTPC where I do not have cable service for it. Perhaps there have been some hackers busy developing an open-source community to enrich the feature set -- I can always wish :-)

No. These boxes are "locked down" fairly well. There's no way to load your own software on the box.

If you want your own DVR for off-air, you need to look at the DTVPal DVR and TivoHD. If you want your own DVR for cable, then you need to look at the TivoHD and Moxi.