I was severely disappointed with the Asus Zenbook when I got it many months ago- not due to the 4gB of ram, but rather the keyboard. It was unusable.
I had been waiting for the right Ultrabook to come along that could match the Zenbook's Sata III, excellent resolution & form factor, and come with a usable keyboard. At CES, I found it. The Samsung Series 9 2012. 1600x900 resolution on a 400 nit (super bright, awesome viewing angles) panel w/ i5, supporting Sata III (or so I was told), 2.5lbs, .5" thick, nice battery, gorgeous form factor, awesome keyboard - etc.
Now that it's finally out, I did some research and decided to go for it.
I found this:
Which is a Samsung rep clearly stating that the NP900X3B (B for 2012, 3 for 13") can take 8gB of ram. Awesome!
So... it came yesterday. I opened it up. Really looks like the RAM is soldered underneath the metal grate, doesn't it?
I noticed this post gets a decent amount of traffic. If you are still seeking an ultrabook with 8gB RAM, consider the new (NP900X4C) Samsung Series 9 15". It has the brightest screen of any ultrabook (400 nits), is only 3.6 pounds and .58" thick, and has a 10 hour battery life. I wrote up a teardown of it here.
I actually upgraded mine from 8gB RAM to 16gB RAM.
I also wrote up a comparison of the Samsung Series 9 to the Macbook Air on my other blog.