Unfortunately, I'm using a laptop. Also, with the gnome setup, were you able to get panels on the second screen?
I run KDE on CentOS/RHEL 5.3 with a dual monitor setup on an nVidia 8800GT card. It runs great. I run Ubuntu on my laptop, so I haven't tried a dual monitor setup on that, though it does have an nVidia video chip set in it. I might see if I can run a dual monitor setup on that with the LCD and an external display.
All that said, it did take me awhile to get it working the way I wanted. I had to hand-craft the xorg.conf file, though new distributions, such as Ubuntu are not supposed to need or use the xorg.conf file for X configuration. Supposedly the new Xorg server is smart enough to figure out what to do... That assurance and about $3.50 USD will buy you a nice small double cappuccino these days.
Well, in my experience on Ubuntu, it is. It just took a single tick box to get the dual monitor setup working and everything, so no messing around with xorg.conf, but Gnome didn't throw panels to both the screens, so I found it a bit hard to use (that might be because I was running Netbook Remix though)
I would expect that netbook remix wouldn't have very good dual monitor support.
Every time I have setup dual monitors or have seen a dual monitor setup the xorg.conf has to be modified at least some. It's not to hard to setup. A few google searches should find you some information.
I don't think that I have every seen a multiheaded setup with gnome panels across multiple screens... You might be out of luck there.