It's human nature to thank someone when they help you: Comments, Upvote and reputation constraints. StackOverflow prevents you from from adding comments or upvoting until you have some experience with the site as indicated by reputation, and I support that.
I think it would be beneficial for both answerers and newbies if the upvote button were converted to a "Thank You" button when you don't have enough rep to vote. The thank you's would be tallied and displayed somewhere, but they wouldn't affect rep or answer order like votes. It gives the newbie a way to engage with the site and register their gratitude, and it gives the answerer another source of warm fuzzies.
Bonus points if you could figure out a way to convert a thank you to an upvote once the issuer has earned enough rep.