Is it worth the extra cost? It depends on what it is worth to you. If I gave you the Pepsi challenge (or anyone really) that had two identical systems side by side but one had generic RAM over Corsair RAM I would say most people could not even tell the difference.
If you are into extreme over clocking and want to reduce bottle necks and like to heat sink and fan cool your RAM then, I'd say it may be worth it. When I built my system last year I did it with 4Gig of Corsair RAM, not because I thought it was better but because it was on sale and the same price as regular RAM and it came with the heat sink/fan attachment just in case I ever felt the need to over clock.
Look at their warranty too, I believe their warranty is life time, which is a good thing considering RAM can go bad due to any kind of power spike in your computer.