Actually, on that note, ReplayTV 4504 versus Pioneer TiVo DVR versus original Series 1:
Series 1 wins for hackability, hands down.
The TiVo remotes (both peanut style) are very friendly, almost enjoyable to use.
The ReplayTV wins for network features out of the box. The UI is very annoying, though.

I want the best of all worlds. Too bad I can't have it.