this post is an answer to Varis comment, also note that I haven't been using the PMA400 as long as the 770.
First each device targets a completely different market, while the PMA targets the mobile/portable media player market the 770 is meant to be for mobile/portable Internet usage. These differences are pretty easy to spot: the PMA400 has a build in hard disk and extra hardware to speed up video and audio decoding and comes with recording software, the 770 comes with Bluetooth, a web browser and news reader and offers way better connectivity.
In terms of being the ultimate carry around device I really can't decide, there are just these significant differences which would make me vote for both devices. I terms of size/form factor and battery runtime I would defently prefer the 770 (sorry Matze and Frank!).
Finally I guess both devices are already outdated, since rumors are out that both companies have been working on new devices for some time now. I can't wait to see what they have come up with to impress us even more!?!