Does anyone know if there is a significant weight difference between the 2011 13" MBP with the stock 320 GB HD, and the weight of the same model with the SSD upgrade? I am considering portability as a major factor for an upcoming purchase, and am deciding between the 13" MBP (w/SSD) and 13" MBA. Will upgrading to SSD shed any significant amount of weight from the listed 4.5 lbs. It seems that all of the comparisons/reviews only discuss the entry level MBP w/ the standard 320 GB Serial ATA HD. There's not a whole lot of discussion with the SSD upgrade - other than to acknowledge the increase in overall speed. Any insight is appreciated.