I'd say it depends on your system. If you don't have dual channel, then definitely go for it. If you do, then it gets more complicated. If, for example, you have 2x256MB right now in dual channel, then adding another 512MB and running it single channel won't help you much. On the other hand, if you have a single stick of 512MB, and add another to run in dual channel, the performance difference will be huge. I'd say, if you're stuck on single channel or need another stick to run dual channel, go for it, but if you would be losing dual channel, then wait until you can afford a 2x512MB or 2x1GB upgrade.
Anyways, the bottom line is that if you plan to keep your system for a while, 512MB won't cut it. It's already looking slow in Doom3 and other new games, and the gap will grow in the future. You're gonna have to get more ram eventually, when just depends on your situation (dual channel, number of slots available, price, and types of games played).
Anyways, the bottom line is that if you plan to keep your system for a while, 512MB won't cut it. It's already looking slow in Doom3 and other new games, and the gap will grow in the future. You're gonna have to get more ram eventually, when just depends on your situation (dual channel, number of slots available, price, and types of games played).