+1 for having retainers act as personal messengers/ah assistants/general currier! Like a nomad moogle, they deliver mail if outside a city and send stuff to the AH for you.(to sell only. who would trust a retainer with a credit card?!) With a cool-down timer of course depending on where you summon them from (it can be a long walk back to the city!).

Do this on a test server first! Not sure how the system would like all those retainers running around. But it sounds nice...

I think SE was hoping to create a real city atmosphere with the retainer system with "faces" rather than icons and numbers to interact with. Grand as that may be, they failed to remember that it was a MMORPG and not a mall.