Right now, the Lync client will download the address book at a randomly chosen interval between 5 minutes and 60 minutes after sign-in. This can be controlled via the registry in a method described at http://policelli.com/blog/archive/2011/03/16/how-to-force-an-address-book-refresh-on-lync-client/. I think it would make more sense to make this part of the client policy.
Idea No. 222