If you want to run Lightroom then don't look anywhere near netbooks. I have a netbook and thought it would work fine for a little device to review images on the road. It's unusable. Lightroom just isn't designed to run on that spec machine.
You'll need a real laptop. I just went through the whole process of trying to find one for photography work and here's a couple of quick thoughts:
Lenovos have rock solid reliability. I've had them through work several times and they're excellent (with the exception of the recent W510, I have no idea what they did to make the trackpad on it so awful, but it's awful).
Dells are cheap but variable reliability. My experience (and those of others) is Dell's initial product quality is highly variable. You may open the box and have a lovely laptop. Or you'll open the box and have a non-working wireless card and a chip in the screen (as my wife's did). But Dell will fix it fast, and then the laptop screams. Oh, and they're *cheap*.
I just bought a Dell XPS 17" (way bigger than a netbook!) with 8GB of RAM, Intel Core i7-2720QM processor, 500GB drive (really irrelevant since I'll be swapping out an SSD and drive from my existing laptop), 1GB NVidia video card, Blue-Ray DVD reader, DVD/CD writer, 9-cell battery, and 17.3in 1920x1080 display. Total cost, including tax and shipping? $1360.77. You can spec out a similar Dell XPS 15" machine that won't be so gigantic in size for less.
!!!
A comparable Lenovo will be right around $2000, based on my research.
Neil