I've been meaning to link to my friend Jason's rant that TiVo doesn't really get podcasting for a couple weeks now. Everything he says is spot-on.
I played with the dual tuner TiVo a couple months ago and it was the first time I got to play with the podcast tools. Like Jason, I was very disappointed to see the TiVo client seemed to rely on the network for everything. I couldn't get most podcasts to play due to slow downloads and I couldn't believe the pause/fwd controls were disabled.
After using it, I would guess that adding podcasting to the TiVo OS was something tacked on, maybe pushed through by marketing, and the engineers that worked on it didn't take the time or care to do it right. It's really surprising, since with the large hard drives in TiVos these days, caching and saving a few megabytes of audio and allowing basic operations on those files should be trivial, not to mention the dozens of open source podcast libraries that demonstrate how to do it right.
Hopefully future versions of the TiVo OS will remedy this -- it definitely feels like a disconnect when TiVo handles large video files so well, but is nearly useless and buggy when it comes to simple, smaller audio files.