I got the 13-inch: 2.26GHz and i upgraded to 4GB Memory and a 250GB hard drive. I'm so excited but since I upgraded its taking forever for apple to ship out my new Mac. I'm supposed to get in on the 21st, I'm used to PC's so I'm nervous but I also have had lots of problems with them and I'm excited to try something new. Is there anything important I should know about making the switch from pc to mac?