So, as is always the way, some Bad Eggs have attempted to spoil a nice thing for everyone. As is, I'm sure, open knowledge - if you refresh an old character, you'll get the achievement XP for age and login time again. This wasn't intentional behaviour (as in, it wasn't specifically designed to be like that), but I liked it and so didn't change it.
Alas, some people have been Taking Advantage of that, and so it's had to be changed a little. Now, you cannot spent achievement XP on learning from another player until you reach guild level 75. Achievement XP can be spent at the guild as before.
We will be keeping an eye on the situation, too...
EDIT, 03/02/2009: This turned out to be clunkier in practise than I would like, and so it has been changed, as outlined in a more recent announcement.
Drakkos |