Hi Marketoid,
The Google link: functionality hasn't behaved properly for a year or two now, but there are some quite neat ways to check competitors backlinks. This is an entire industry in itself though! And it really depends on how much time and resources you want to dedicate to this. Firstly, some of the quick methods: a Google search that worked well in the past (not quite so well now, but still will return some interesting results) is:
sitename.com -site:sitename.com
Into the Google search bar (list all pages that contain sitename.com that are not from sitename.com). If this works it will return some links and generally some of the better ranking ones near the top - and the poorer ones lower down.
The problem with this method is it now returns also just sites that contain text sitename.com (may not be actual links). If you find this happening it would be worth trying "sitename.com" -site:sitename.com (with quotes) and is also worth trying with the www form if you don't have any joy with the above.
As Clicky Leap already mentioned you have SEOMoz's Open Site Explorer (
http://www.opensiteexplorer.org/) which has a reasonable tool there, but one I found that is particularly effective is Majestic SEO (
http://www.majesticseo.com/). Despite the name, they actually work very well, they have their own crawlers and have been going longer than Open Site Explorer. You can analyse your own sites backlinks with this for free, but would need to be a paid user to analyse competitors backlinks. This will also alert you as to when the links appeared - and will present the information in all sorts of interesting ways.
Getting links in all the places your competitors have won't necessarily guarantee you will outrank them for the same searches, but can be excellent way to get additional ideas of good sites you might get additional links back to your site.
Good luck!