I have a Series 3 and dual tuner Series 2, connected via ethernet. They can share shows, but the Series 2 cannot download the S3 HD recordings. You can start watching during the beginning of a download assuming you've got a fast link. 802.11b may not be fast enough to allow it but 11g will. You can still transfer w/ 11b but it'll be a little slow. I've used my Tivos w/ those Netgear Powerline adapters because I wanted wired, not wireless. It was pretty fast.
If you have an iPhone or iPod touch (or iPad...), you can use DVR Remote with a Series 3 or newwer. This allows you to use your iPhone as a Wifi remote to your Tivo. It's WAY faster than an IR or RF remote because the commands are sent via the network, not IR. Response is almost instantaneous, including entering a 3 digit channel, including the ENTER key. This would allow you to have an easily configured Wifi remote.
Another option is to get 1 Tivo and 1 Slingbox. Then you can use a PC/Mac in another room to stream that Tivo. The Series 3 has both the HDMI and component out simultaneously, so you can use one to the Slingbox.
