I ordered a new AirPort Extreme base station to stream content from my Mac Pro to the AppleTV at 802.11n speeds. The rest of my wireless network I'll keep at 802.11g via my current base station (since neither my MacBook Pro or wife's MacBook supports 802.11n anyway). Using two separate wireless networks, I can keep one at full G speed and the other at full N speed, without slowing the N network by also making it G-compatible.
I've got an AirPort Express attached to each of my two TiVos. I'd love to be able to transfer recordings at 802.11n speeds, rather than 802.11g speeds (which is actually has a pretty slow real-world transfer rate, even in g-mode only, without b support). And buying an additional $179 802.11n AirPort Extreme for each TiVo ain't gonna happen. A $99 AirPort Express N and I'd strongly consider it.