With the Series3 installed, we now have two ways to easily listen to podcasts on our main system. We can either use FrontRow on the Mac mini, or use the podcasting application on the TiVo Series3. There are good and bad things with both of these solutions.
The podcasting application has a small directory of audio podcasts. The ones you want to have easy access to, you can mark them as favorites. For the podcasts that aren't listed, you can, tediously, enter the urls of the rss feed with the remote. Playing back works by essentially streaming the audio file.
Since FrontRow is essentially a frontend to iTunes, you can use the whole iTunes podcast directory to find and subscribe to podcasts (including video podcasts). When a podcast is not listed, you can also enter a url to a rss feed. (Unfortunately, you can not do either of these with the remote, but you have to use the keyboard and mouse.) iTunes periodically downloads the latest episode of the subscribed podcasts, so play back just plays the local copy.
Personally, I like playing audio podcasts through TiVo's interface. The main reason is that I keep getting bitten by the bug that I mentioned before. If you don't listen to a podcast, iTunes will stop downloading new episodes. So if I listen to the podcast on my iPod (attached to my MacBook Pro), the podcasts on the Mac mini will stop updating. For video podcasts, FrontRow is the best solution, as TiVo's podcast application doesn't support video.