I got a little over 13Gb back on my RevB SSD. Just did the update from DVD.
Before and after
You gained about 7 GB of space just like everyone else. Nobody truly "gained" the space they're reporting.
I keep seeing all these people report that they gained anywhere from 13GB to 28GB of space back, but they're all seriously incorrect.
Snow Leopard counts the size of the disk differently than Leopard. This has been reported elsewhere, yet everyone keeps reporting how much space they "gained," even journalists who reviewed Snow Leopard.
Check your disk's capacity. It went up by 8.3 GB. You're not really recovering that 8.3 GB of space... the portion of your drive being used by your OS, apps, and files is still the same. So, an app or file that supposedly took 1GB of space before is now taking more than 1GB of space.
The more space someone reports "gaining" back is directly related to the size of the HDD/SSD. Everyone is really getting approximately 7 GB of space back. The rest is all disk reporting size differences between Leopard and Snow Leopard.
Instead of checking how much "available" space, people should be calculating the difference in how much space is being used versus the percentage of drive space that the used amount is. They could then calculate the true "gained" space.
The capacity change doesn't truly gain any space, it's just a way the disk is reported. Do a Google search and read about it.