@Tokaaa:
It would seem Kuma's powers do, in fact, have to do something with one's desires, not just wherever he wants them to go. Perhaps it's asking the question that makes one think of something, and based on that idea they are sent to a place that Kuma seems fit or simply a place that matches those wishes.
Nami to an island that would give her more knowledge of the weather; helping in both her fighting style and navigating in the new world. Fairly obvious.
Franky is sent to technology island to gain knowledge of… well.. fairly obvious. Will help him being strong and will probably upgrade his body as was done with pacifistas.
Usopp is sent to one of the most dangerous islands seen so far; probably because of his desire to become a brave warrior.
Zoro is sent to where Perona is -- the creator of the one of the only beings he cannot cut or withstand.
Chopper is sent to an island that relates to animals. Probably plenty that he can learn there, but we don't know enough on the island.
Robin is sent to something directly related to the void century. Will probably give her some knowledge on it and, with a bit of luck, buff her up to bodybuilder size so that her DF will become much more usefull.
Sanji is sent to Okama island, where he probably either learns how to accept people for what they are in the inside and blablabla, learns okama kenpo moves, or simply gains a load of leg strength. This, too, because he wants to be stronger.
Brook is sent to some place we know fuck all about, too soon to say anything about it, etcetc.
the first part of your post seems to contradict the second?
Anyway I disagree! Firstly that he can send them to where they desire, if stated by them, but its clearly not the case with the crew. If it was about desires then why did Sanji land in the KammaBakka kingdom? why didn't Nami land on some treasure trove? etc.. etc..
Also what you don't take into account is the speech with Raliegh moments after sending them to thus destination?
http://www.onemanga.com/One_Piece/513/11/
My view is that he can send them to any place, but chose to send them to islands appropriate to their talents, in the knowledge that they were capable of regrouping and becoming stronger/more talented.
We know Kuma's view of the crew from thriller bark, we know he has a bigger plan, and we know the islands were obviously chosen for a specific reason. People like Perona and Moria were of no interest to him, so instead of choosing their destination, he asks…..'Where would you like to go'. But with the crew he doesn't ask because he has already decided, this means he has pre-planned something for the crew. He said that he had doubts about his actions against the crew, but he still proceeds to send them to their destinations knowing that his plan still stands a chance. Even Raliegh appears to stop trying to help after speaking to Kuma. Doesn't all this hint at a bigger plan, rather then his showing up just to send them to some dream vacation?
Conclusion: Kuma can send people wherever he wants, if he asks them then it would appear they are sent to that destination, but if he has a destination pre-planned then there is no need for the question. Simple