In the end, it depends.
If you are running several memory intensive applications you're going to want more swap space. At the very least, you should have as much as your RAM because when you hibernate it takes all the pages in your RAM and puts it into the swap space before powering off your computer. I wrote about this a while ago:
http://www.bytetrap.com/blog/2008/06/02/swap-space-linux/
In the end, it depends. If you are running several memory intensive applications you're going to want more swap space. At the very least, you should have as much as your RAM because when you hibernate it takes all the pages in your RAM and puts it into the swap space before powering off your computer. I wrote about this a while ago: http://www.bytetrap.com/blog/2008/06/02/swap-space-linux/