Depending on what model you get, the Optical drive sometimes runs on a slower bus compared to the hdd slot. If your interested in an SSD, i'd either put it in the HDD bay and take the hdd out completely, OR put the ssd in the primary hdd bay, then get a bracket to put the old HDD in the optical drive slot. From memory the brackets aren't that cheap though. Also making those kind of changes as soon as you buy it instantly voids your warranty. May be worth just paying to have the ssd upgrade done when you buy it. Or consider the retina 13" model, as it is based on a flash storage architecture which is very fast.