Facebook usage is just off the charts - September Nielsen Data
Top U.S. Web Brands and Parent Companies for September 2009 | Nielsen Wire
The average U.S. Internet User — that’s the AVERAGE USER — spent nearly 5.5 hours last month on Facebook. 105M total U.S. users use the site.
Top 10 Parent Companies/Divisions for September 2009 (U.S., Home and Work)
RANK, Unique Audience (000), Time per Person (hh:mm:ss)
1 Google 153,928 2:36:52
2 Microsoft 136,639 2:08:38
3 Yahoo! 134,688 3:08:28
4 Facebook 105,449 5:24:38
5 AOL LLC 89,302 2:40:19
6 News Corp. Online 86,290 1:30:36
7 InterActiveCorp 70,900 0:18:33
8 eBay 65,285 1:24:37
9 Wikimedia Foundation 61,321 0:17:29
10 Amazon 60,397 0:22:44 Source: The Nielsen Company
And, check this out. The typical U.S. Internet user spent 68 hours online in September (both work and home combined). Of that Facebook accounts for 7%.