I'm not experienced with Linux, so I wouldn't even consider anything too tricky. I also required OpenOffice and other similar tools, so that ruled out some others.
Ubuntu was a contender, and for a user like me there's much about it to like. But I wanted Linux for my Thinkpad X41 precisely because XP Pro was chewing a huge proportion of the battery life just booting up. To my dismay, altho' Ubuntu obviously boots a lot quicker than XP, total battery life was even worse.
I know, there are things you can do - but you have to want to do them. I wanted the laptop to work effectively with the least interference from me, that's all.
So when I discovered that Mandriva (with one small tweak - turning off Bluetooth at boot) could deliver c.25-30% longer battery life, it was an easy choice.