Count me impressed. I use netbooks a lot and FF4 gave me the best browsing experience I've ever tried on a 10"-screen, Atom-CPU powered PC. Performance improvements and the amount of space it saves on a small screen for my usage are pretty amazing. Kudos Mozilla for another great release!

EDIT: Just noticed that FF4 allows me to resize text-fields that render quite small because of the small screen. Small, relative-sized text-fields can be easily resized to a convenient size.