The i5 is last generations' architecture, is rated at 35w, 2.53ghz, turbos to 3.06, and has the hd 2000 graphics. The i7 is the newest architecture, is rated at 17w, 1.8ghz, turbos to 2.9, and has hd 3000. Both are dual core with hyper threading.
Is it worth it? I don't think so. The i7 is better(only slightly) but unless you moved to a quad core like the new macbook pros have, it's really not much of a performance difference. http://ark.intel.com/compare/54617,43544