The first, and honestly, the only Linux tweaked for netbooks I've used is Ubuntu Netbook Remix (UNR). Intel's Moblin for netbooks didn't seem as interesting during my brief testing period (testing was brief because I didn't like it :-). I admit that Ubuntu Moblin Remix looks more interesting, but I have not tried it yet.

However, if you have an older pre-Atom netbook, neither UNR nor UMR will scratch your netbook Linux itch. I just noticed a Linux distro that seems to be running on old netbooks like the Asus Eee PC 701 or 900 in various YouTube video demos...

eeebuntu

However, there are also demos of it running on the Atom-powered Eee PC 1000.

If you've been running Eeebuntu on a netbook for a while, let me know how it is working out for you.