May want to check out Tom's hardware guides and look at the SSD vs. HHD benchmarks before you drop that sort of cash.
BTW, the MB's come with 160 and 250 gig hard drives standard. The 320 is a BTO option. Why are you going to spend more money on an optional hard drive when you're planning on immediately replacing it?
Maybe a better bang for the buck would be a 7200 rpm notebook sata hard drive, like from WD, Seagate, Hitachi, etc. You can find them online for roughly a hundred bucks or so, and IMO you'll be able to tell a difference in bootup times, cold application launches, transferring larger files to disk, etc.
I think what a lot of people are doing is waiting for the price per gig and storage capability of the SSD's to improve before they shell out that sort of money for that little storage. Then again, there's a lot of people on the boards who're saying they're getting one now.
Unless you've money to carelessly burn through, do your research and make a well informed decision. Good luck!