I chose the 2.26GHz MacBook, 2GB memory but would like to upgrade to 4GB. I can order online but I'm a little bit eager. Now, my local store says that they have them ready in stock and can install the 4GB for me. (will take 2-3 hours) Problem is this is my first Mac purchase and I don't know if I should do that. Should I go for it? Any bad experiences or anything I should know about? Thank you for your help.