I would say wait unless you really WANT SL now. The truth is SL is problematic for a lot of people. Lots of people have reported fans going nuts and MBAs overheating. Others have apps that are crashing. There have been reports of doing common things like saving a file and OS X failure.
I really wanted to install SL so I did. But I honestly think I regret it. While it is faster by three seconds on startup and shutdown is nearly instant. However, Xbench is reporting something like 35 point reduction??? My CS3.3 isn't supported and have been several problems reported.
Snow Leopard doesn't seem ready for 64-bit kernel. The rev B/C are fully 64-bit CPU, EFI, and drivers are there. But Apple decided to not allow 64-bit kernel on the "consumer" Macs. I think that's BS. But here's the thing, people that do boot into 64-bit kernel are having problems! Their Macs slow down to a crawl.
It really seems like Apple rushed this at the end. Apple didn't even write drivers for Macs sold two years ago. I would be most pissed if I were those people as they will not be taking advantage of the very things Snow Leopard was designed for like OpenCL.
Lastly, the biggest problem with SL is that there are no third party apps currently taking advantage of OpenCL or Grand Central. It will probably be a year or two before SL technologies are being used. And I have read a few things that say Macs with 2/4 GB of RAM do not benefit from 64-bit apps in the first place.
I think two years from now my 2.13 GHz MBA with SSD will be far more capable than it is today because of the advancements of Snow Leopard. But for right now, Leopard may be the better choice.
I am seriously considering doing a reformat and clean install of Leopard. Then switch to Snow Leopard when it makes more sense. But I am going to wait and see what happens before I go through the hassle. Maybe 10.6.1 will help and maybe we will learn more about when future apps will take advantage of SL technologies...