Maximum PC

for a total of 2gb.

2x1gb
Overclocking
Upgradeability
Less chance of a bad dimm

4x512mb
Performance

Someone a while back linked an article that showed a slight performance increase when filling all four slots. That's the only article I've ever seen on such a thing, and I personally prefer having less sticks when possible.

Wow...simple question, but it really is hard to find an honost answer. Maybe it's all just preference?

It used to be an issue that 1G sticks had horrible timmings and was better to go to the smaller capacity modules. With DDR, that may still hold true to a point, but is slowly becoming a non-issue with DDR2 (don't even bother thinking about it yet if you run an AMD system).

As far as upgradeability, I like the idea of running with 2x512 and THEN decide if you want more. If so, then buy a couple more. The 1G sticks are highdollar items indeed, and I highly doubt the need for more than 2G's of memory. I still haven't found the need to plunk down more peso's for another Gig of the stuff.

You're milage may vary, but since this is in the Gamer's Arena I'll advise based on game usage alone.