The Pop Down Project (which I discovered via the utterly magnificent Pop-Up City blog) marks "annoying advertisements, signs, objects etc. with the x-button sticker to make them pop-down. Will they disappear? Obviously not, but it’s a nice idea of connecting digital life with offline activism." Apart from this merry slice of slacktivism, do check Pop-Up City's other posts, e.g. this one on trends for 2011 or these on biking in the city.
http://pop-down.blogspot.com/
http://popupcity.net/2009/02/the-pop-down-city/
http://version1.itsnicethat.com/index.php?id=1727
http://www.ifeelasphalt.com/index.php/2009/03/02/pop-down-project/ (source of quote)

Cars into bicycles (2010) by Folke Koebberling & Martin Kaltwasser (with the students of the Art Center College of Design), on a car parking lot at Bergamot Station, Los Angeles, USA.
http://www.koebberlingkaltwasser.de/cars-into-bicycles--the-californian-dream.html
via http://flavorwire.com/123734/daily-dose-pick-recycle
viz. http://www.sweeney.ucr.edu/exhibitions/recycle/
see also http://www.sweeney.ucr.edu/exhibitions/recycle/_pdf/ReCycle_Catalog.pdf

Antwerp & Ghent: so far so good, though mostly for lack of cameras ;-/ ... whereas in Brussels ... Worldwide: see http://www.mybikelane.com/ ... All this via the ever excellent BDW!

Biker Byrne also organises biking tours, designs bike racks and has published his "Bicycle diaries" in 2009.

Bonus (für David) : http://flavorwire.com/92002/whats-special-about-these-crazy-bikes + http://uzine.posterous.com/ride-your-vinyl-get-on-your-vinyl-and-ride

And Bulgarian inventor and engineer Martin Angelov is experimenting with flying bicycling lanes! "Of course it is too early to talk about mass use." Tnx Crachàt!