Got one of these babies yesterday. I still don't really understand who and what exactly they're meant for, but they're cool! The pricing is moderate (300EUR+taxes at Nokia's webstore) and the performance is quite decent.
The 770 is basically an embedded Linux box, based on an 220MHz ARM CPU with 64MB RAM. There's also 64MB of available built-in flash memory and an RS-MMC slot. Display is 800x480 (16bit color), allowing decent web browsing over 802.11b/g WLAN or Bluetooth with the built-in Opera.
The coolest thing is the OS: It's based on Debian and it has a fresh kernel. You can actually log in to the tablet (after installing DropBear SSH) and it'll say something like:
~ $ uname -a
Linux Nokia770-43 2.6.12.3-omap1 #1 Thu Oct 27 09:24:21 EEST 2005 armv5tejl unknown
There's also a whole new development movement going on to produce software on the Maemo platform, which is used to create applications for Nokia 770 and other compliant devices. The platform is based on GTK+ (and the Hildon Application Framework), so you'll be coding fairly familiar looking programs in C. And they're distributed as .deb Debian packages. None of that Symbian mess with endless class hierarchies and special binary files!
Native Maemo applications will be using the Hildon framework to provide a graphical user interface with menus, toolbars, dialogs, etc. Console applications can also be used after installing an XTerm. This includes stuff like irssi (the IRC client), GAIM (IM client for MSN/AOL/ICQ etc) and AbiWord (word processor). Check the Application Catalog at maemo.org.
A brief word on the performance. I'm surprised how smoothly this device works. There are some delays when starting applications, but e.g. scrolling a webpage is very responsive. Could it be that Nokia has finally matched a software platform with appropriate CPU power?
Anything to complain about? The screen is small. You have to hold it pretty close to surf the web at 800x480 resolution. And how come they couldn't use the same standard power adapters as every other Nokia phone does?