I have 2 Gigs in my macbook. I do photoshop as well as lightroom (both at the same time). Sometimes I get bogged down. Can't seem to find a definate answer on whether the limit is 2 or 4. If I do get four, how great of an increase in boot times, and my usual editing, etc could I see. I have heard with some computers the increase isn't that great and sometimes not worth the $. Thank you, you guys are always great help.