I have a recently purchased Toshiba netbook and did some multitrack recording in Reaper with it...but the interface I used is perhaps not what you're thinking of. I already had a Zoom H2 recorder...it can be used as a USB mic but I actually used it as just a USB interface - I plugged my guitar into a Sansamp GT2 and then into the line-in of the H2 and monitored the input and recorded tracks through the H2's headphone jack.
It all worked out fine - although I admit that my test was just a very short 30 second doodle with about 5 tracks overdubbed without plugins running on them. I also got Addictive Drums running on it, but I had to render the drums to audio in order to overdub without latency. I did have to adjust the buffers in Reaper to get the latency to a manageable level. Make sure to turn off your wireless and firewall/antivirus.
I'm actually surprised that I got this far with it...this netbook's specs would be considered laughable for a DAW: 1.6 GHz Intel Atom, 1GB RAM 5400rpm hard drive with a USB interface...not exactly cutting edge firepower.
One flaw in the test: there is a bit of a leak between the monitoring and the input signal on the H2. So when the guitar input is silent, the tracks playing back leak into the input. It's a very weak bleedthrough so I wouldn't say it's a complete dealbreaker but a better USB interface should be cleaner than this. I have read someone report that the ultra-cheap Behringer UCA202 has this bleedthrough problem also so I would stay away from that one. In the end I wouldn't get the H2 for its USB interface ability although it's fun that it can used that way.
Good luck and I'd love to hear what you wind up with.
