Is a memory upgrade worth it?

RAM is always something you can never have enough of. (Of course being reasonable and not putting outrageous amounts for the heck of it.) Its one of the easiest upgrades you can do and memory prices have come down drastically in the past couple of years. It should not only give you more performance but you should also get a slightly longer battery life. (You have to access the hard disk less) I would even suggest looking at getting one 2 gig stick to add to your 512 megs. Although getting only one additional gig would still greatly increase your performance.

Yeah, with RAM prices being so incredibly low (DDR3 aside), it's almost always a good idea if you can fork up the cash.

I'd even go as far as not using your 512 stick, since chances are newer RAM will have better timings, but you can only go as fast as your lowest common denominator, so you might end up buying low timing sticks, but having to use high timings because of your 512.

1x 2GB stick if your system can support it or 2x 1GB

The other thing to keep in mind is that most laptops only have 2 DIMM slots, so the likelihood of you being able to reused the old stuff with the newer stuff isn't very high. With RAM being so cheap, I agree with the others to just bite the bullet and get a 2gb kit.