Pros of Linux:
1) It's free (as in freedom) software. You have the freedom to modify it as you see fit, or if you yourself don't know how to, you can at least ask a programmer to do something for you to improve it. This can't be said for Mac OS X or Windows.
2) It's very stable and reliable. Many web servers run Linux, and don't get restarted for months if not years.
3) It's free (as in costs no money).
4) It runs very well on underpowered or older hardware.
5) The 'distribution' (just a packaging of lots of programs together to make a usable system similar to Windows), usually contains a web browser, word processor, spreadsheet program, games, etc.
Cons:
It's a different system to Windows, so while there is a program called wine which can be used to pretend to be Windows, there's no guarantee a Windows program will run under Linux. But usually there's a Linux version or similar program that works just as well.
It's also different to Windows in some ways, so may take a bit of time to get used to. It's no harder to use, just different.
Basically, I think it's worth trying out, and if you only use it for the kind of things netbooks are recommended for, you'll find it great.
What are you planning to do with it?