I removed my battery for the first time yesterday when I replaced the hard drive and the memory.
It is amazing how quick and easy it is. MacBook, 3 screws pop the new stuff in, screw it back up and you are done. The Aluminum iMac is even easier for memory. Pop out the one screw pull out the old stuff, pop in the new, screw up and you are good to go.
The only hurdle I did come into was installing Leopard (I wanted a clean install). I only have the the upgrade to Leopard so I had to first install Tiger, then upgrade to Leopard. Once I had Leopard up and running though I just connected the MacBook to my iMac using FireWire, reset the iMac holding down T, and the MacBook saw my iMac drive and then copied about 100GB of data across which took just over an hour
. I could have tried the Gigabit ethernet which is even faster, but the FireWire was fast enough. I love my Macs lol.