2. Updated often
3. Software is free (usually)
4. More control over the system
Linux is secure, so far, but only 6% use linux. If more people used it I'm sure more bugs / exploits would turn up. But then the linux staff would just write a patch for it
Instead of wait 3 months (like some other operating system)
One big disadvantage though, if you don't know much about linux it's going to be hard when you start and you'll probably be tempted to format and stick windows back on.