Definition of Rating:
If it does not work for users, it's not useful. While on the surface this may seem an obvious sentiment, understanding user experience and designing for target user populations are critical. In addition, it is important to recognize that in many cases users will not expend the time or effort to interface with a system that is demanding of them. It is important to keep these factors in mind when choosing a participatory technology.


Rating Scale:
* no sign up, no sign in and surf
** Registration or payment required
*** Significant time commitment required

Category	PMCA	Rating
Multi-Media Sharing		*
	Flickr.com	* - **
	YouTube.com	*
	.mac	*
	Veoh.com	* - **
	Blip.tv	*
Social Networking		**
	Facebook.com	**
	MySpace.com	**
	Friendster.com	**
	Ning.com	**
	Twitter.com	**
Blogging, Vlogging, Vcasting, and Podcasting		*
	Blogger.com	*
	Livejournal.com	*
	Wordpress	*
Wiki		* - **
	Wikipedia	* - **
	Wetpaint	* - **
	PBWiki	* - **
	MediaWiki	* - **
	Socialtext	* - **
Social Bookmarking		*
	del.icio.us	*
	digg.com	*
RSS		**
	web-based	**
	client-based	**
Virtual Worlds		***
	Second Life	***
	there.com	***
	Koneva	***