This was discussed in a previous thread (go figure) and specifically in relation to BF1942. I have read of these curiously long load times and whatnot but have not experienced them with 512MB. 20s or so seems the norm (I have not timed it but even the largest map can't take any more than 30s). So I still think it is due to slow HDD's or fragmentation, or something that I thought of since -CD checks, since I use "virtual CD" images. Game play is as smooth as butter made from baby's bottoms (network willing).
The Task Manger -> Commit Charge -> Peak tells you how much memory was used so if it is more than the physical then you know that HDD paging was necessary and more RAM may be a benefit. Now, since getting into the DesertCombat mod again recently I have noticed that it definitely would benefit from more RAM as my CCP is over 750MB with all the usual crap running in the background and also it is evident during game play, most notably at the start of a new game but still with the occasional hicup during play. I guess it uses more because it is loading all the original as well as added files. Maybe it would be possible to create custom trimmed down RFA's and such if you only played DC -or maybe if they eventually sell it as a stand-alone it will not be such a hog. But I do plan on getting another 512MB.