I expected the x40 to be the same as the x31, but 0.9 lbs lighter (assuming the 4-cell model). The main difference, based on specs, is the inability to use standard 2.5" drives, meaining you can't get a larger capacity drive or a faster drive, such as the 60gb 7200rpm model.

Any problems, issues, etc.?

Published specs for battery life are 3.5 hours for the 4-cell model and 7.5 hours for the 8-cell