During our second Disney trip and first with DMIL & DFIL (who were not hard core lovers like us until then ) we encountered a beyond wonderful CM at HS (then MGM) named Jessica. We were soooo appreciative of her and her helpfulness I wanted the higher ups to know. So when we got home I wrote a letter singing her praises (that experience was also the one that solidified our desire to vacation there forever and join DVC). Off I sent it just wanting to brighten their day as I'm sure they hear negative more often than positive and I got a phone call thanking me for the letter and letting me know that they had shown it to both Jessica and her supervisors!!! How great!!!!
I agree, member services or guest communications should not only be used for negative complaints. We send 2-3 letters after every vacation to either member services or WDW guest communications complimenting cast members or things we liked on our trip. I feel that positive feedback goes a long way, and its always nice for a CM to get a good letter in the file.
Just this week, after our not so good DVC experience, I sent a complaint letter to member services, and 2 letters of commendation about CM's to WDW.