I remember a few months back (before 10.5.6 was released) a number of people were having problems with their aluminum MacBooks when they upgraded their RAM themselves. Some non-apple-provided RAM was causing kernel panics, lockups, and other serious issues (issues which would disappear as soon as the RAM was removed). People were speculating that it was because the nvidia chipset in the MacBook is very picky, so any differences in latency or other tiny differences from Apple-provided RAM would cause issues. I haven't heard anything new about this issue lately. Has a system update fixed it? I'm asking because 4gb RAM is now cheap enough that I am getting very tempted, and the upgrade would really help me out.