Probably about 99 thousand threads on this exact topic. But ill be nice and still answer.
Yes it does.. Not right away but give it a couple weeks of use and youll see your iphone performing like a turtle.
Do yourself a favor, go on 3.1.3, JB, Unlock.. Install SBCatagories (= apple folders)
Backgrounder (= Apple multitask) - only you can enable/disable this as you please so you wont see performance issues..
Problem solved.