Sorry for the OT but no-one else I know owns a Mac

Simple one, what is user upgradeable in a MacBook? By user upgradeable I mean can be done without voiding the warranty. I've downloaded the manual and it looks like just the memory. Can someone please confirm this?
I'm going to order one today for the wife and was going to get the base model then upgrade the memory later myself (considerably cheaper than Apple even if using the identical Kensington memory units) but if the HDD and optical drive aren't upgradeable then I may go for the next model up even though I begrudge how much extra they want just for an extra 30GB HDD space and to write DVDs!
That and I'll need to share this MB until I order my MBP in January...
Thank,
Martin.