It should backup with your google account. Mine always pops back up after re-syncing after I do a fresh install..

@Double0EK
I don't see a specific option for wifi network backup under account settings...
I need a sure fire way of saving my networks. I have lost them and started from scratch too many times :(

Titanium Backup is supposed to offer this in its free version according to their website. I've never tried. Eighth feature of the free version on this page. http://matrixrewriter.com/android/

Edit--->Just for fun Iinstalled TiBa and when you go right to the bottom of the backup restore list there is an option to back up wifi access points. But like I said I've never tried it...

OK, so this is what works for me....

1. I restore the wifi access points from titanium backup. Just as a test, I deleted one network from my list after backing it up.
2. Restore through titanium backup. Wifi network will still not be present.
3. Reboot the phone, and the network should be back in the access point list :)
   

I'm assuming this will work whether you're restoring one or all of your wifi networks.
Google does not sync or backup these networks.... I have never experienced that, throughout all the ROMS I have flashed over the past year (yes, my account sync is on)