Originally Posted by khuon
Like many bike manufacturers, Specialized has a house brand for components. Most of these components are rebadged OEM products that have a markup for the brand name applied. A lot of times, manufacturers will take relatively low-end OEM components and mark/hype them up. In this case, it would be better to go straight to the component manufacturer and by the no-label version. In many cases, for the money of the bike brand name component, you can find an aftermarket brand name that's of higher quality. Specialized's brand isn't necessarily bad... it just might not be as good as others for the same money. Hell, Specialized may even in fact be rebadging USE seatposts for all I know.
^^^ What he said...
Didn't mean to post and run! Specialized make great frames and sell fantastic bikes (heck, we've bought two new Specialized bikes in the last 8 months), but personally I'd usually look elsewhere for component upgrades for exactly the reasons Khuon mentioned.
Unless you're prepared to spend some pretty decent dollars, it might not be worth the upgrade as you possibly won't notice all that much difference.