Here are the 20 Largest Social Bookmarking Websites ranked by a combination of Inbound Links, Alexa Rank, and U.S. traffic data from Compete and Quantcast. Although no traffic metrics are completely accurate we do believe the data below to be useful for gauging relative audience size.

1 | twitter

760,750,806 – Inbound Links | 23,579,044 – Compete Monthly Visitors | 28,000,000 – Quantcast Monthly Visitors | 13 – Alexa Ranking.
Top 20 Social Bookmarking Websites | Updated 3/5/2010 | eBizMBA

2 | digg.com
383,598,000 – Inbound Links | 33,433,760 – Compete Monthly Visitors | 11,400,000 – Quantcast Monthly Visitors | 183 – Alexa Ranking.
Top 20 Social Bookmarking Websites | Updated 3/5/2010 | eBizMBA

3 | Yahoo! Buzz
20,031,000 – Inbound Links | 8,119,906 – Compete Monthly Visitors | 3,600,000 – Quantcast Monthly Visitors | NA – Alexa Ranking.
Top 20 Social Bookmarking Websites | Updated 3/5/2010 | eBizMBA

4 | tweetmeme.com
422,863 – Inbound Links | 18,244,542 – Compete Monthly Visitors | 2,300,000 – Quantcast Monthly Visitors | 1,898 – Alexa Ranking.
Top 20 Social Bookmarking Websites | Updated 3/5/2010 | eBizMBA

5 | StumbleUpon.com
234,000,000 – Inbound Links | 4,418,609 – Compete Monthly Visitors | 1,100,000 – Quantcast Monthly Visitors | 362 – Alexa Ranking.
Top 20 Social Bookmarking Websites | Updated 3/5/2010 | eBizMBA

6 | reddit.com
161,685,000 – Inbound Links | 4,908,990 – Compete Monthly Visitors | 1,300,000 – Quantcast Monthly Visitors | 441 – Alexa Ranking.
Top 20 Social Bookmarking Websites | Updated 3/5/2010 | eBizMBA

7 | Technorati.com
175,287,000 – Inbound Links | 3,309,174 – Compete Monthly Visitors | 2,000,000 – Quantcast Monthly Visitors | 662 – Alexa Ranking.
Top 20 Social Bookmarking Websites | Updated 3/5/2010 | eBizMBA

8 | del.icio.us
427,665,000 – Inbound Links | 1,623,083 – Compete Monthly Visitors | 317,000 – Quantcast Monthly Visitors | 2,476 – Alexa Ranking.
Top 20 Social Bookmarking Websites | Updated 3/5/2010 | eBizMBA

9 | kaboodle.com
2,600,000 – Inbound Links | 3,941,212 – Compete Monthly Visitors | 2,500,000 – Quantcast Monthly Visitors | 1,694 – Alexa Ranking.
Top 20 Social Bookmarking Websites | Updated 3/5/2010 | eBizMBA

10 | mixx.com
16,005,000 – Inbound Links | 879,108 – Compete Monthly Visitors | 2,200,000 – Quantcast Monthly Visitors | 645 – Alexa Ranking.
Top 20 Social Bookmarking Websites | Updated 3/5/2010 | eBizMBA

11 | Propeller.com
5,725,000 – Inbound Links | 1,164,549 – Compete Monthly Visitors | 624,000 – Quantcast Monthly Visitors | 1,801 – Alexa Ranking.
Top 20 Social Bookmarking Websites | Updated 3/5/2010 | eBizMBA

12 | newsvine.com
71,708,775 – Inbound Links | 1,142,779 – Compete Monthly Visitors | 1,300,000 – Quantcast Monthly Visitors | 5,545 – Alexa Ranking.
Top 20 Social Bookmarking Websites | Updated 3/5/2010 | eBizMBA

13 | Fark.com
36,162,723 – Inbound Links | 652,762 – Compete Monthly Visitors | 1,300,000 – Quantcast Monthly Visitors | 4,119 – Alexa Ranking.
Top 20 Social Bookmarking Websites | Updated 3/5/2010 | eBizMBA

14 | Slashdot.org
37,566,035 – Inbound Links | 862,416 – Compete Monthly Visitors | 404,000 – Quantcast Monthly Visitors | 970 – Alexa Ranking.
Top 20 Social Bookmarking Websites | Updated 3/5/2010 | eBizMBA

15 | twine.com
343,090 – Inbound Links | 1,062,304 – Compete Monthly Visitors | 188,000 – Quantcast Monthly Visitors | 19,592 – Alexa Ranking.
Top 20 Social Bookmarking Websites | Updated 3/5/2010 | eBizMBA

16 | clipmarks.com
461,141 – Inbound Links | 379,354 – Compete Monthly Visitors | 507,000 – Quantcast Monthly Visitors | 6,330 – Alexa Ranking.
Top 20 Social Bookmarking Websites | Updated 3/5/2010 | eBizMBA

17 | dzone.com
3,867,009 – Inbound Links | 281,098 – Compete Monthly Visitors | 208,000 – Quantcast Monthly Visitors | 7,002 – Alexa Ranking.
Top 20 Social Bookmarking Websites | Updated 3/5/2010 | eBizMBA

18 | faves.com
1,437,453 – Inbound Links | 159,051 – Compete Monthly Visitors | 244,000 – Quantcast Monthly Visitors | 6,198 – Alexa Ranking.
Top 20 Social Bookmarking Websites | Updated 3/5/2010 | eBizMBA

19 | blinklist.com
51,912,576 – Inbound Links | 86,650 – Compete Monthly Visitors | 44,000 – Quantcast Monthly Visitors | 10,985 – Alexa Ranking.
Top 20 Social Bookmarking Websites | Updated 3/5/2010 | eBizMBA

20 | diigo.com
8,933,453 – Inbound Links | 146,144 – Compete Monthly Visitors | 30,000 – Quantcast Monthly Visitors | 7,569 – Alexa Ranking.
Top 20 Social Bookmarking Websites | Updated 3/5/2010 | eBizMBA