The Google Link: operator causes a lot of angst among newbie webmasters. The purpose of the operator was to find all the links that link to a particular URL or web page, but more recently it only shows a small random sample of all the links that Google knows about and uses. Sometimes that small random sample contains no links. It is not a problem.
To use the operator, simply type link:http://www.yourdomain.com into the search box and you will get the sample that Google shows for that URL. Do not try to use this for any sort of analysis or interpretation or to compare with your competitors.
There should also be NO space between the ‘link:’ and the ‘http://www.yourdomain.com’ to use the operator. If you have a gap, you may actually find more actual links to the site, but with the gap, you are actually just searching for pages with the word ‘link’ and ‘http://www.yourdomain.com’ on them and not actually using the operator. Again, do not jump to any sorts of conclusions about what this may or may not show.
To get a better picture of your backlinks, sign into your Google Webmaster Account.
For more on the use of the different operators in Google, see this Google page. See this on the Google link: operator.