2GB or 4GB RAM Macbook Air

If you use as you stated, then 2GB should be sufficient, however, you should test the 2G model at an Applestore before you decide (you will notice this most with Aperture). You cannot upgrade the RAM on the Air later. Also, only you know if 128G is enough storage space based on what you're using now (I had to move my iTunes Library to an external drive when I purchased my 11" with 128G).

Since you can never expand the memory, and I firmly believe you will expand the usage of your notebook, seek out the 4 GB unit. The 2 GB sustems seem like a good deal, because the demand is so much lower, and that is the price that gets them sold.

Lion itself is fully functional on 2 GB, but add in some applications and you really notice it dragging for a far greater reason than the balance of the unit's specifications.

The amount of disk space can be managed much more effectively. So if you have to skimp, do it there. Later on, you can consier expanding disk space, or offloading some data to external sources.

I have a maxed-out MBA, b ut if I had to lose anything temporarily, I would give up SSD space.

I have a Macbook Air 2010 13" and have 2GB RAM. At that time I opted for the bigger SSD a 256Gb then more RAM because I knew I would not run a lot of RAM intensive apps. I have not been sorry, even after upgrading to Lion. The only time I can see more RAM then 2GB would be if you plan on running Parallels or Fusion virtual software with Windows 7. That combination needs all the RAM it can get. In fact I believe even Parallels now recommends 4GB min for Windows 7.

Caution: the MacBook Air with the 1.86 GHz processor has probably a previous generation (late-2010) Core2Duo CPU. 2 GB RAM is also a bare minimum. You'll get more lifetime out of your Air with 4 GB of RAM.

The mid-2011 MacBook Air has a Core i5 processer, which at 1.7 GHz is considerably faster than, e.g., an 2,13GHz Core2Duo CPU (i5 CPU supports 4 virtual cores, and has a faster memory bus than the previous generation Air). The new MacBook Air also has improved power management and efficiency (i.e. it runs less hot when displaying multimedia, or doing some more heavy computing).

If you need to save money, check out "Apple Certified Refurbished" on the Apple Store web site of your country. The refurbished Oct 2010 13"-model (2.13 GHz, 4 GB RAM, 256 GB SSD), e.g., is currently €1199 (incl. tax) in the German web store.

I'd go for the 4GB unit. I find it absolutely hilarious that, when the MBA only had 2GB of memory, the vast majority of the posts whined that it could not be upgraded. Now that the MBA can be configured with 4GB of memory, many posts complain that the users can't figure out which memory configuration to purchase.

The OP isn't dealing with a $100 RAM upgrade decision