So you think with 2gigs I will be fine?
Depends on your definition of "fine".
Will you be able to launch a VM, run Windows and some applications? Yes you will.
Will you wish you had 4GB? Yes you will.
Will you kick yourself for not getting the upgrade? Maybe, but maybe not. It depends on your usage in many ways.
Personally, I run VMWare Fusion pretty much all day at work. I bounce between OS X and Windows apps all day long. At this moment, I have 2 versions of Visual Studio, SQL Server management studio, IE (yuck) and OneNote open in Windows. That's about normal, and I don't really feel like I'm taking a big performance hit from a dedicated system, except when I do things like launch a debugging session or otherwise start compiling things - moving around in editors is fine. In OS X, I generally have several browser windows (Safari, Chrome and Firefox all at once usually) all with many tabs per window, mail, Word, Excel, sometimes Eclipse and maybe a text editor (UltraEdit).
I have a 2008 15"MBP with 4GB RAM, 2.8 C2D and an Intel SSD. I think this is very comparable to the new MBA - the only thing that's somewhat faster is the CPU. My workload pretty much fills up 4GB RAM most of the time - currently I have 48MB 'Free Memory', although I do have 734MB "Inactive". I would NOT want to try this on 2GB RAM and I would really LIKE to have more then 4GB; however, for me, 4GB is exactly adequate.
If you keep less stuff open than I do, 2GB may be adequate for you, but I could never recommend less than 4GB for anyone who intends to run Fusion or Parallels as part of their normal work load.