Not an ultra; but I was looking for something similar, I think to what you were looking for.
Small, but still useable, light, fast, good build quality and hopefully cheap.
I did a alot of research and watched slickdeals.com regularly for deals and ended up with an Asus 1215b with an E-350 processor. It comes with 2gb of ram, but I put another 4gb stick (22$) to bring it to 6; and replaced the hard drive with an ssd ($100).
all in all I have about 450 bucks into it and it's great. Everything works in linux; but graphic drivers aren't quite upto snuff. With windows 720p played fine; on linux it is sometimes jumpy; even with hardware acceleration.
It has no optical drive (a feature for me). It also has usb 3.0 which was a must-have for me.
Main downside is that the touchpad has a flaw and you have to fix it yourself. If you are going to put in an SSD anyway (and you should/have to) you will beable to fix it while you are doing that. Otherwise its like a 5-10 minute fix depending on how comfortable you are taking apart laptops.
The other big downside is that replacing the hard drive voids the warranty (or at least, you have to break through a sticker that says if tthis sticker is broken the warranty is void).
But all in all I am super happy with this laptop. The function keys work, the wireless is solid; with an SSD it boots up in seconds; everything is lightning fast. Only a dual 1.6 ghz so if you are doing lots of heavy compiling it isn't probably not for you.
I have not done much gaming on it; I have played a little bit of heroes of newerth on ultra low settings and it was playable.