Pico is a modified version of WordPress' first magazine-styled (and still one of the most iconic) theme, Mimbo. It retains Mimbo's layout and functionalities, and is loaded with a lot of new, useful features.
Pico is designed to run without any tweaking needed. Just upload and activate! You can and are encouraged to dig deeper into Pico's more advanced features (like Widgets or Page Templates) when you need them, but they're all optional.
Pico supports WordPress 2.9 Canonical Post Thumbnails. Don't have time to set it up? No worries, because Pico can fetch the first image on your Post and use it as a thumbnail instead. Heck, you can be lazier and have no image. You won't get a thumbnail, but the layout will still look juust fine.
The original Mimbo has 1 Widget area. Pico has ten. Need I say more? You even get four Widget areas on footer, and there's also the more prominent Spotlight Widget area, where only your most important widgets should go.
*Because it totally is.
Mimbo's most iconic feature is its Featured Categories area on the left sidebar area of the home page. Pico turns this neat feature into a Widget, so that you can now place it somewhere else: you have ten different areas to use!
Pico retains Mimbo's custom Archive List page, with two additional Templates: List Authors and Sitemap. Stay updated, because more is definitely to come!
Breadcrumb navigation is a way to ensure your visitors not to get lost while exploring deeper into your site. Showing up on top of any single Post, it shows them their current position inside your site and gives quicker access to go back. Pretty neat.
So you love replying to comments on your site? Of course you do. Pico supports threaded comments up to 3 levels deep. You just make sure to enable threaded comments on Settings > Discussions and you're good to go!
(Won't be that hard. Promise.)
The top category navigation area says "Category" under each Category's name:

You can change it to anything you want by going to Post > Categories on your Dashboard and start editing the Category you want. In the Description textfield, insert your own text (keep it short and concise!) Once done, it will automagically show up on the navigation area.

If you don't use it, you won't see it. Place any widget into the Pico Spotlight Widget area and bam! You'll have that widget placed right on top right area of your blog, prominently displayed in a box with a strong background color:

The purpose of this area is to draw more attention to it, so put important things and call-to-actions here!
Pico uses a 16 columns grid for its design. Hit Alt + Shift + G to show and hide the grid guide, pretty useful when you're tweaking the design on your own!

(P.S.: You can try that shortcut combination on this page, too. If you need practice or something.)
Pico is known to work on the following browsers:
Pico requires the following for it to work:
(Without Whom There'd be No Pico.)
Darren Hoyt made Mimbo theme. If you open up Pico's PHP files in a text editor, there's a 98.3782% chance that you'll see his original code. Don't forget to check Pro Theme Design, which houses the awesome-er version of Mimbo: Mimbo Pro.
Ian Stewart made Thematic theme. The very small percentage of code I put into Pico is probably originated from his theme. Also, the various Widget areas idea is taken wholesale from Thematic.
Justin Tadlock made Hybrid theme. A lot of Pico's neat features are from his theme, say the Page Template and breadcrumb functionality. Also I've spent countless of hours reading various WordPress tutorials in his site, all of which are amazingly useful and highly recommended.
These guys made one of 2009's best themes, Basic Maths. The grid show/hide functionality is taken directly from it.
Andrea gave this theme the name "Pico", which is for the best because left in my own hand I'll probably name it something silly.
From the guys who contribute to Codex, to those writing tutorials, plugins and themes. Thank you for all the sharing.
Download Now! Version 1.0.5 — January 7th, 2010 Subscribe to wplover I couldn't possibly hand-deliver you theme updates, right?
(Yes, I put the download link down here so you'll take the time to read the Credits first.)
Various wplover articles that more or less talk about Pico (or part of it):
Comments? Questions? This way, please.