I have to say i actually love this idea. When I started in my first guild a similar system was in place for guild "noobs" and my current guild carries on this tradition. It is simply a case of making it more global and less exclusive.
Of course there will be issues with trust, scamming etc, as will all aspects of the game but honestly guys do you really think Ent hasn't thought of that, credit the guy with some intelligence he has already proved he deserves it.
I do like the idea of an NPC, not to "run the show" but in a similar role to gossip and her pvp service, it makes both parties more confident in the transaction. I also agree that a small gift of some kind is appropriate as a thank you but this should be down to the discression of the mentor, after all the more you give as a thank you the more likley they are to want to do those "boring" jobs you really don't want to do.
Thanks to Emerald and Storm for spell checking for me, its late and I need coffee
Wolfy