Some of those comments seem to suggest that removing the battery doesn't stop it losing power :( However, I will try making sure I switch off the webcam and wireless before shutting down. I know to turn them off while the Eee is running to save the battery life (you told me that) but I hadn't thought about while it's switched off.

The batteries definitely degrade quickly, even if you don't get a dud. Mine still gives me around 5 hours, but the capacity is dropping noticeably. Do let me know how the bigger battery works out!