For me, it was not about money (didn't save much anyways). I actually waited till after the 2011's came out because I planned to get the new one but ended up disappointed with the changes.
So anyways.
I bought a 2010 13" (1.86ghz/4gb/256ssd) a couple days after the 2011's came out and I like it a lot. Before the air, I used a 2010 15" high-res MBP and a core i3 Thinkpad. For what I do, the Air actually performs better because of the SSD. Even though the processor is older and "slower", it's not noticeable for anything I do.
I use it for business school and also do some light web design. For a lot of good reasons, I prefer the 2010 over the 2011. If you need extra power (HD video editing maybe?), then I guess the 2011 is better but if not then get the 2010 for sure.
Some good things about it:
+Snow Leopard
+USB installation drive (used it once already & would have smashed my computer having to download OSX)
+Runs extremely cool (why get a warmer running computer if you're not using all the power?)
+Better battery life
+Better video card
+I never use backlit keyboard, even when I have it. (that's one feature my dad loves but I could care less)