We checked out the rumors back in March and checked out the official announcement back at E3, but tonight we finally get a chance to check out the Check Mii Out channel for ourselves.
Upon the first load, the channel asks you to pick a Mii to serve as your "artisan," as sort of signature for any Miis you might choose to share. After that you can choose between two main sections. In the Posting Plaza, you can check out a random assortment of Miis from your region or around the world, and also the most popular Miis as picked by other users. Any Mii you like can be given the "I like it" seal of approval, or be copied and imported directly to your Mii channel. You can also post your created Miis in this section for evaluation.
In the Contests area, you can upload Miis based on certain assigned themes -- the first contest asks for your best "Mario without his cap." Once the contest is done in six days, you'll be able to pick out your favorite entries and view the results.
It's easier to understand if you see it rather than just reading about it, so check out a quick video after the break.
[Thanks to everyone who sent this in.]