I find the idea of Luis von Ahn great and really unbeatable!!!!
On the Web you have so many people who like to do all the sharing kind of staff, writing journals, Wikipedia's articles, blogs :-)
Why don't give them a job?! Why don't create the applications that make the boring tasks and tests quite interesting, challenging and entertaining?!
I want to enlighten in my blog the Web applications that I found interesting and "games with a purpose" that I found challenging and useful!