There are friendly uses for 301s and some not so friendly!! 
One use is for scripts that use 301s to place cookies to keep members logged in as well as other things. The cookies keep the login info from page to page.
I believe that Joomla and E107 use them as well but don't quote me.
You can also re-direct domain names which uses a 301 to get to the destination point
which is very commonly used BTW!!.
As long as a 301 is used in a friendly way they cannot hurt you at all in the SERPS!
How do you check?? 
Go Here: Search Engine Friendly Redirect Checker