1) Syntax: link:www.your-domain.com or link:http://www.your-domain.com
DO NOT use space after link:
will show the backlinks of that page which Google knows and decides to show with that command
will show results that contain the text "link" and the text "www.cnn.com"

2) Google doesn't return all backlinks in response to link: command.

3) Google link: command is not updated in "real time" but it is updated approximately once per month

4) Since June 2004 Google returns backlinks which have any PageRank value (and not only backlinks which have a pagerank of 3 or 4 or more as Google used to do)

5) To get more accurate and up-to-date Google backlinks you may use the following command
:www.cnn.com Remark: not all results return by this command are links to www.cnn.com page, it can be just a plain text URL (www.cnn.com) without links mentioned on the page somewhere
:www.cnn.com -site:www.cnn.com This command will show you all the pages linking to cnn.com, minus the pages from cnn.com site.

6) Related Google links tools
Google backlinks and anchor text analyzer
Google ranking software (based on Google API)

7) Articles related to Google link: command

Google backlink strategies

Hope this may help you!