That's when I use Coat;
Actually the recommended mini-Moose is now Mouse, it was written by and maintained by one of the core Moose contributors and unlike Coat it is commited to stay 100% compat with Moose (it even has a module Squirrel which will choose Moose or Mouse depending on if Moose is already loaded or not). This is of course not to say that Coat is a bad choice, only that the author has decided compat with Moose is not as important to him, so if that is important to you, then use Mouse.
Here's hoping Moose makes it into 5.12 Core (but not likely!)
Here is hoping it doesn't!!
When a module goes into the core it suddenly has a dual-life. There is the (frozen) version that is distributed with the latest version of perl, and then the (living) version that is on CPAN (you now, the one with the bugs fixed and new features). Not until Moose is completely bug free and feature complete will I allow it to get put into core, in other words, it is never going to happen :)