When to use Parallel.For?

I have recently moved to C#.net 4.

I love Parallel.For, but not sure when to use and when not to. I know that when order is not important for me - I'll use it.

But are there any tests regarding the overhead of working with Parallels? Meaning, if my loop runs only 10 times (and performs very little logic) - should I avoid Parallels? Are there any thumb rules?