Pinterest is hot. If you haven't read at least one article daily about how the social sharing startup has already crossed 10 mm MAU, is more engaging than every other website besides Facebook and Tumblr, and is apparently driving more traffic to retail sites than Google+, then you've been living under a rock. Or at least not in silicon valley.

So what makes Pinterest work? While some people have their bets on shady viral marketing tactics, you cannot deny that Pinterest is an incredibly engaging product. 

Also, while I agree that Pinterest is fundamentally a curation app, I don't think the "curation motive" alone drives this engagement... though it is a big factor.

Here are some of my thoughts on what makes Pinterest so engaging:

1. We are visual animals.

Pinterest is highly visual. In essence its a visual Twitter. Its a simple micro-sharing app where the content you share is not 140 characters of text but an image. As as we all know, images always win over text in engagement... humans are inherently visual animals. Photos are also much easier for our brains to process and react to (like, comment).

Even the simple actions on Pinterest are the visual equivalents of their Twitter counterparts: Retweet = Repin, @reply = Comment and Favorite = Like. But instead of navigating techie syntax, users get visual cues (aka UI) for each action, making them much more approachable and easier to engage with.

And to top it off, the continuous scroll interface gives you an endless (literally) amount of visual porn so you never have to leave, making the site highly addictive.

2. Constrains are an equalizer.

Again taking a page out of the Twitter and Instagram books, Pinterest constrains all pins to the same size (195 px wide, height adjusted to maintain aspect ratio) and column layout. Whether you pin a photo of the interior of a beautiful home or of a shoe, the pins are the same size and are given the same treatment on the site. And just like the 140 characters constrain of Twitter or the square format with filter of Instagram, this brings a sameness to the content, making it an incredible equalizer. It allows everyone to contribute without inhibition... even if they are not a professional blogger (Twitter), photographer (Instagram), or tastemaker (Pinterest.)

3. Closing the consumer-participator gap.

Pinterest turns the classic social-media-user-segments pyramid on its head; or more accurately, evens it out. On Pinterest, its super-simple to go from being a consumer to a participator by Liking or Repinning an item. True, Pinterest didn't invent either. Facebook probably deserves the credit for making the Like button ubiquitous, and Repinning is much like Retweeting or Reblogging on Tumblr (its more akin to the latter.) But where Pinterest wins is making these actions, *how* you consume content on the site: using Pinterest literally means browsing around (endlessly - see above) while liking and repinning items as you go. There is nothing else to do on Pinterest, and that turns out to be a very good thing.

Whatever the reasons for its awesome growth, this is definitely going to be the year of the pin! Oh and one more thing... if I were working on product at Pinterest, my focus would be on building a killer iPad app. iPad is the perfect medium for Pinteresting.

Facebook Places has been around for way too long now for its poor UI and inconsistent experience to be tolerable. The launch of Places hasnt changed my behavior one bit - I'm still an active Foursquare user - but for all the people who are using Places, Facebook really needs to update some basic stuff. 

The biggest annoyance is the fact that unlike all other check-in or local-business discovery apps, Facebook still has not bothered uploading a basic local business directory into Places. This means that unless someone has manually added it - no Place you check-in to has an address, phone number or any other information except its GPS lat/long location displayed as a pin on a map. Here is a screenshot of what my nearby Martha & Bros coffee looks like on Facebook Places vs. 4sq. As you can see the 4sq version has the address and phone number of the business.

This is bad enough on mobile, but when you're on Facebook.com its an even funkier experience. Facebook often promotes recent Places check-ins by your friends. Depending on what information is available for which business, you can get a number of inconsistent experiences:

1. zero address info - if you were browsing around and landed on this, you dont even know which city or country this place is in.... i just landed here through a FB-promoted link.

2. some user-inputed info - this at least shows the correct city, but its clearly been entered by some user as you can tell from "the mall!" description text.

3. address info - some lucky businesses get their address in there somehow.

C'mon Facebook... even a tiny startup like @Matchpin has all standard business listings available in the app for users to select from, with pre-uploaded address, GPS and phone numbers. I'm sure you can manage this.