@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.
Whilst that may be true for some scenarios (like if you do something stupid like allocate space for a pagefile in the RAM disk), for others it will have a beneficial effect. Storing something on a RAM disk means that it never touches the real disk, so a RAM disk might be ideal for storing lots of intermediate files which for some reason must be written out to somewhere - for example if you're taking a photo and passing it through lots of small programs each of which does a transform to the file and then writes it back to disk, then a RAM disk would speed things up just because you avoid all of the file flushes going out to disk.
Similarly, playing a hi-def movie from a RAM disk would effectively guarantee no skipping of the movie compared with running from a hard-disk or CD-ROM because the content doesn't need to be loaded or streamed into memory - it's already there.
I think the important point here, though, is that it all depends on how you use the RAM disk. If you're careful you might get a speed up compared with just letting Windows do it's thing (because you know what you're going to want to do more than Windows can guess what you're going to want to do), but in practise you'd probably get a bigger bang for your buck by just giving all of the memory to Windows and reducing the strain on the pagefile.