Dual core will show your average Joe an advantage in only one area (but boy is it a biggie): multitasking. Having 2 cores is logically the same as dual cpu's, which means that 2 threads can be processed simultaniously. If your running just one process, you wont see any improvment (but I challenge you to find a PC that belongs to someone not technically inclined that has less than 20 processes running
) When you have word, IE, your anti-virus, an IM client, Itunes (sucks lol), ad-aware, and god knows what else running at the same time, you will see one hell of an improvment.
Edit: I forgot to mention all the damn MS processes that run by default, along with those pesky auto start apps like the ones that make my mom's pc crawl (until I clean it every other month)