I was in the Costa Mesa, CA store the other day and, for kicks, asked them about upgrading the RAM on my MBA. I told him I bought it a couple weeks ago and asked if it was possible to upgrade the RAM.
He said sure, not a problem. They'd buy back my RAM and then install the new RAM. Kinda made me think they would replace the mother board by that statement.
Then I told him that I'd heard the RAM was soldered in and couldn't be replaced. He said he had to double check. Walked into the back, came back and apologized and said I was right. He said he never did it on the MBA and that you can't replace the RAM.
I don't know if all the stores have the 'Ultimate' in stock but he did say they carry the fully loaded MBA.
So, I'm 18 days since purchase and stuck with 2GB. Oh well. I've adjusted and I'm peaking at about 60% or my RAM during the day so hopefully that'll hold me over till a MBA refresh comes out and maybe I'll replace my MBA.
I've actually noticed that if I just don't pay attention to my little istat RAM monitor, I see no difference in speed. It's still perfectly snappy for me.