It's more or less exactly the same with contemporary programs. You'd notice it more with video or photo editing, I imagine. Games are only now starting to take advantage of it.
On the other hand, you can have like 100+ porn videos open at once.
But I already am using contemporary programs. It's not like I stopped updating iTunes, my web browsers, or any of my games. I'm using old versions of PhotoShop and Microsoft Office but that's it. A lot of that software already feels sluggish. I'm wondering if upgrading RAM would make any difference. Not to mention the CPU -- I'm upgrading from a Q6600.