As has been mentioned, the 360 is missing a lot of nice features around recording and usability (many of them TiVo patents, so wont be coming in the future), you do get a couple more apps (though obviously only if you pay to subscribe to them) and voice control.
Some of the missing features are as follows; Wishlists (where you can set the box to record programs on certain subjects or featuring certain people), undelete, series link+, series link manager, suggestions, setting of series links for programs not in the current TV guide, ethernet control, keyboard support via USB, switching between tuners with constant buffering on all tuners, skip-back on fast-forward, quickplay, default recording options, cancelling individual recordings from a series link, multi-channel series links, radio channels allowing recording of radio, separation of recordings between boxes, watching recordings when internet is not available and probably a few others I've forgotten.
Also, extra boxes do not have their own hard disks or tuners (unless converted from a V6 box), so you lose storage space and recording ability and are also reliant on the main box being on to watch and set recordings and also on having a decent wi-fi signal (or ethernet cable) between the two boxes when watching recordings. If the boxes are used by independent family members i.e. older children living at home, then there is also the issue of recordings being pooled across all boxes, so everyone's recordings are mixed up, rather than being separated. This also means that if there is a show that both people watch and one person watches and deletes it then it is gone for the other person as well, and can't be recovered due to the lack of undelete.
