I am buying a PS3 soon. Not enough money for an 80GB. What are drawbacks to buying the 40GB?

I am looking to buy a PS3 very soon. I don't think I will have enough money to get an 80GB. Probably will settle for a 40GB. What are the drawbacks of doing this? Can I upgrade the memory later? How does the lack of the extra 40GB effect gameplay or performance? Is resale value going to be significantly less?