this may seem a very silly question, but is the ssd slot an 'external' storage slot? i have the 120GB and to save space i store my music and movies on my external WD HDD which is plugged into my wifi router, it has readyshare built in and alows my mac to easily play those files over the wifi. but..if i could buy an SSD card....do they just slot in flush or do they stick out like a USB stick? im abit confused with these SSD cards because the info i'm finding for them are SSD 'replacement' cards...or swapping you HDD for a SSD etc. so, can they just plug in nice and flush to increase my storage?