@VIad: If you have a RAMdisk, some of the RAM is not usable by Windows, ergo swapping happens more often. Except that in this case you're needlessly copying data from one bit of RAM (the RAMdisk) into another bit of RAM (the memory left for Windows). In effect you're storing duplicate copies of lots of things in memory and occasionally copying them around for no good reason. This hurts performance in comparison with simply using the RAM as RAM.

If you put more memory in a PC, then allocate a large chunk of that to a RAMdisk, as per the article you linked to, you will quite possibly see some performance increase. It's just that it will be less of a performance increase than simply putting the same amount of memory in and letting Windows allocate it as needed.