I don't have a netbook, but I do have a laptop that's about as small as one (10.something" screen), and whilst I have read on it I find it far less comfortable to read on than my Sony, and the positions I can read in are more limited. In fact for comfort, and despite the much smaller screen, I'd sooner read on my Nokia N800 than the laptop!
The downsides of it, compared to my Sony (and my N800, for that matter):
Short battery life
Awkward to hold for any length of time
Not many comfortable reading positions
However, if you can only afford one, and you need the netbook and only want the ebook reader, then get the netbook now and keep an eye out for cheap readers for later. You can read on the netbook, it just may not be as anjoyable an experience as on a dedicated reader.