Bukkit

The upcoming release of 1.7.6 (and above) will be using UUIDs instead of player names since Mojang will be adding the ability to change player names soon.
It is very important that Privileges implements this as soon as possible to prevent any issues from arising.

http://forums.bukkit.org/threads/psa-the-switch-to-uuids-potential-plugin-server-breakage.250915/

I am already aware of this and I will release an update as soon as it is necessary.

I think "now" would count as being necessary, name changes are expected today.