I've had my Nokia 770 for a little over a week. On Monday evening I managed to pry it out of my girlfriends hands for long enough to try running one of the first old GDK C apps that I wrote. Although the app worked fine in the development environment it failed on the device itself due to assumptions about having 24 bit colour depth.
A simple source code change from using gdk_pixbuf_render_pixmap_and_mask(a,b,c,d) to gdk_pixbuf_render_pixmap_and_mask_for_colormap(a,gtk_colormap_get_system(),b,c,d) solved it.
The unit is very cute and got a lot of attention when I showed it off last weekend; but there are a few niggles - the biggest is a lack of a docking station. It's also far worse at picking up the weak wireless signal in the house than the Orinoco pcmcia cards.