Man that's outdated. SWAP files are supposed to be a substitute for not having an adequate amount of RAM, so the more RAM you have, the SMALLER your swap should be. The 2x rule was outpaced a while back but people are still quoting it.
What it comes down to is this, how much RAM do you want to be able to address in Linux? If you've got 1024 megs of RAM, don't make a swap file (unless you *really* need it for some reason) and you'll always be running at high speed as the swap file won't be needed. If you've run Windows and found a 'comfort point' for your Virtual Memory, use that as your swap size. Myself, I've got 256 megs of memory and run all my swaps @ 256 megs. I've never had an out-of-memory error in Windows or Linux.
Stolid