Couple of things I find important in laptops (not just netbooks):

-Keyboard size, screen size, and mouse type (pad, stick, both): Consider how much time you will be spending using the device at one sitting, and ensure that you are comfortable using the device for that amount of time.

-Windows 7: (As mentioned previously) General Availability is set for October 22nd. Most vendors "should" have most/all of the new models on store shelves on that date pre-loaded with Windows 7. Though it might be a month or two before the last remaining Vista PCs are gone. That being said, many vendors are offering free upgrades to Windows 7 on computers purchased now (check first before buying!).

-Data network: Some parts of the world are better serviced by certain providers than others. Plus, your current cell phone provider might provide some sort of incentive if you get additional service for your netbook.