I'll tell you one thing, unless you do basic stuff and don't task your Mac with too many open apps, you will be fine. I have used 4GB RAM since 2008 on this machine and only since last year have I started to see it becoming just about enough for my needs.
Trying to keep the costs down, do you have 4GB, are you happy? Does it slow up? Or is 8GB the way forward.
I run 10+ programs for work with no problem, it never pages out. Apps I use are pretty "light": iA Writer, Numbers, Safari, Marked, Mail, Mou, Skype, iTunes, Dropbox, Skitch. So not everyone needs 8 GB, sure it's not wrong to have more RAM, but NOT EVERYONE needs it.
No, I had 4GB (maximum) on my Mid-2007 24" iMac and had no issues/complaints about the RAM. The Apps I use on my iMac is what I use on my Air.
I only (wanted) to upgrade because it's cheap. My sister who uses her Mid-2010 27" i3 iMac like her iPad has 12GB. Adding 8GB cost me less than $50.
Total 6GB swap in and out and no single bit of lag. I have 8GB and only 40mb of in and out swapping. You should try 8GB; you only know once you tried.
Right, your MBA has a SSD, my MBP has a hard disk which is much slower.