Do great Scrabble players ever turn in their tiles?
Yes, most definitely.  A good write up on exchange strategy can be found in Joe Edley's book Everything Scrabble, pg. 89 and following.  Tournament players do exchange significantly less than they did when Everything Scrabble was first written, since the recent (well, not that recent any more, 2006) addition of QI and ZA to the official Scrabble lexicon have made moves like exchanging only Q less favorable statistically.  However, good players will also know when it is right to "fish," that is, make a nearly worthless play to get rid of certain tiles in order to greatly increase their probability of bingoing on the next turn.  

A great way to get some idea of the frequency with which championship players exchange is to look at some of the games from board 1 of the most recent National Scrabble Championships; all of the games are online in turn by turn form here.  Many of the words in these games will be unfamiliar, but if you want an idea of what great Scrabble players do, that would be the best place to start.

Also, you should note that the best frequency with which players should exchange is going to depend on how large Scrabble word knowledge is (which is almost completely unrelated to your vocabulary).  In other words, based on the words that you know, how soon will you be able to turn your rack into a bingo rack?  If you can't see yourself doing that in the next two or three turns assuming average draws, then you should probably exchange.

The other time to exchange is if any legal play would make your rack worse.  For instance, if your opening rack is AEINQST, your best play by far is exch Q.  Doing so will give you a 95.7% chance of having a bingo on your rack the next turn, and probably even greater than that of bingoing, depending on what your opponent plays.