Definition of Rating System: Traffic refers to how much traffic is drawn to the participatory medium. This is potentially problematic, considering that hits per day and discrete users are not necessarily equivalent - which speaks to the general challenge of devising metrics for online traffic. It is also be problematic in that there may be significant variation between different sites within the same category, e.g. popular vs. little-read blog. Still, an overall traffic rating for the blogosphere and other participatory media offers a general idea of the traffic/user base that they have the potential to attract. Traffic is rated on a scale of 1-10 (1=less than 1 million hits per day/users, 5=40 millionhits per day/users, 10=80 million hits per day/users or more).

Category	PMCA	Rating
Multi-Media Sharing
	Flickr.com
	YouTube.com
	.mac
	Veoh.com
	Blip.tv
Social Networking		10
	Facebook.com
	MySpace.com
	Friendster.com
	Ning.com
	Twitter.com
Blogging, Vlogging, Vcasting, and Podcasting
	Blogger.com
	Livejournal.com
Wiki
	Wikipedia
	Wetpaint
	PBWiki
	MediaWiki
	Socialtext
Social Bookmarking		3
	del.icio.us
	digg.com
RSS		N/A
	web-based
	client-based
Virtual Worlds		2
	Second Life
	there.com
	Koneva