In the last couple of days I did some researching [0] on microstructures / nanoformats which are actually used by applications. Here is my current list in no particular order. Let me know which I am missing.

Dopplr
In dopplr you can post updates of your trips via Twitter. A good example of custom readble microstructures.

A trip to Helsinki on May 19 to May 23 At SFO on September 9th. Leaving on September 20th I'm going to Austin on July 15 for 3 nights


microrevie.ws
Lets you post reviews of anything you like / or not like via Twitter. A review has to be send to @hreview. A semicolon separates what is being reviewed from the opinion. And 1–5 asterisks are used to rate the item.

@hreview Some Great Band; really exciting but too loud ****

Loudervoice Loudervoice lets you review anything you like through different communication channels like Blog, SMS and Twitter. You have to hook up your Loudervoice account with your Twitter RSS feed. And then you can post structured or free reviews:
Review 1 Pizza at Joeys: They just don't get it RE Very disappointed my new cellphone. 1/2
Btw. The free format is human moderated.
Cotweet Cotweet let multiple users of an brand or company Tweet with one account. To distinguish between the users they introduced: ^CoTags, a new convention for using signatures when tweeting from a brand account. It’s really simple—just the carat character followed by the person’s initials, or other identifying set of characters.
@TwilightEarth Glad you're enjoying the Escape Hybrid! Can't wait to see the full review. #FordDrive ^SM

StockTwits With StockTwits you get realtime information about stocks: "A Bloomberg for the little guy". It does that by prefixing the stock ticker with $.
$MCD and $AAPL were ultra impressive today

TipJoy A simple way to initiate payments via Twitter. For example, you can tweet
p @ev $1 because twitter is fun
and send $1 from your Tipjoy account to @ev. And in addition to 'p', payment keywords are 'tipjoy', 'tip', 'pay', 'give', and 'rtip'.
TwitterMap With Twittermap you can update your location:
L:home=517 Spruce Ln, Lenexa, KS 60502 L:lunch:30.010,-90.007



Peqipedia
A micro-pedia which let's you tweet wiki articles like:

@peqi Microstructures = Try to unify the different Twitter formats.


Other links of interest:
Most of the following try to propose a standard but dont' have actual implementations.

[0] Some sources included: http://notizblog.org/, http://www.stoweboyd.com/, http://www.140conf.com/application-directory