Apple considers RAM user serviceable, so upgrading to 4GB wont void your Apple care. Just take the time for a week to monitor your RAM usage. You'll probably

Apple considers RAM user serviceable, so upgrading to 4GB wont void your Apple care. Just take the time for a week to monitor your RAM usage. You'll probably notice that you max out 2GBs a lot. If you do any kind of virtualization, you definitely need 4GB so you can allocate a decent amount of RAM to your virtual machine. If you aren't doing any virtualization... why not? A previous poster is correct that you do need to buy two sticks. Also, I would hold on to your Apple memory just in case. Even though installing your own RAM is ok, you'll want to pop back in the Apple memory before you send it in for service. There's no guarantee they wont swap out your RAM for new Apple RAM while they are trying to diagnose the problem.