Yes, I've had to give my SS# on alot of things i won, some with very little value. and usually i have to get lots of prizes notorized too. One time i had to get a prize with a value of $14.99 notorized. It was for a book.
If you are uncomfortable with giving it out over email (which I would be) ask if you can call them. I would ask them to give you a general office number they can be reached at (rather then a direct line or extension). That way you can have some piece of mind that you are speaking to someone from the company or judging agency. I did this once when I received an email saying I had won $2500. I responded asking if this was legitimate. The guy actually suggested I call the office. I did and eventually I got a check from Travelocity. Anyways, differnt companies have different policies about reporting. Like others have said the $600 is the minimum they are REQUIRED to report. We are suppose to report all wins regardless of the amount on our taxes and so companies are well within their rights to request the information. Others have said they've called companies and gotten permission to omit the SSN from the form for a a small prize.