I'm really enjoying the n770. I'm definitely putting an n810 on my wishlist for the end of this year.
First thing I did was re-flash the device with OS 2007 Hacker Edition, an OS intended for the n800 but crammed into n770 hardware. It works rather well, only occasional reboots, but then again I'm working with a heavily used and refurbished unit. Who knows if it's the OS or the device. Google Talk, contacts, Bluetooth, 802.11b/g, a stripped-down mozilla engine and MPEG4 playback all works well.
I turned my lil' Nokia into a pocket translator with the Google Talk translator bot - the streamlined chat interface of OS 2007 turned the Nokia into a very handy (and quick) translation service.
Also tried to crack a test WRT54G router I have laying around using Aircrack, but I couldn't inject wifi packets using the OS 2007 wireless drivers so had to resort to the slower WEP cracking that needs a fair amount of seed traffic. It was still neat to browse all surrounding AP's on a full-screen xterm. With the n770's fantastic resolution, even the small typeface was definitely readable.
Also been mowing through a number of third-party apps. There is a fantastic developer community around the device - their Sourceforge-like approach to the Maemo Garage and the extensbility of the platform has served the developer and user community well.
It took me a while to find out what type of video the n770 will natively accept. There are several good resources out there, such as Andrew Flegg's Perl script that easily transcodes video into a n770-digestible format. The wide screen and nice resolution make mobile video much more palatable. The only caveat was that newer releases of MPlayer tag video with a newer but much less understood "FMP4" codec tag which OS2007HE doesn't understand. I had to tweak the script to pass the value "DX50" to the ffourcc option in order for the built-in media player to recognize the MPEG4 codec used. I also had to make sure encoding only happens at 15 frames per second, otherwise audio quickly gets out of sync.
When I get a free second I'm going to try getting some OpenVPN binaries to work as well. Would be very nifty to have an SSH stack and VPN access wherever I go.
Got Flash 9 somewhat working, although sound doesn't appear to work. Not a deal breaker tho, considering I'm working on a refurbished device running an unsupported OS meant for an entirely different hardware platform.
All in all, I'm a pretty happy gopher. Not sure what that means, but I am.