Here's how it works: Let's say you want to see all (actually a sample) of the webpages that link to a site you want to investigate. Martinlutherking.org is a common example for this purpose. The query is
link:martinlutherking.org...and the results would reveal the urls of pages that link to the martinlutherking.org home page. This list would contain links from the martinlutherking.org site itself (most sites link to their home page), educational institutions warning about bias on the site (a red flag) and hate groups (another red flag).
Google was the go-to search engine for this until a couple years ago, when they really pared back the number of results they returned. At that time, I advised using Yahoo.com as the search engine. Yahoo's Site Explorer would return many more results than Google.
Within the past few months that has changed. Yahoo merged their Site Explorer with Bing. Now that search capacity is part of the Bing Webmaster set of tools. If I want to see who links to my site 21cif.com, I have to create a Webmaster account, download an xml file from Bing (BingSiteAuth.xml) which the search engine uses to collect data on my traffic, etc. That's 1) not as user friendly as it used to be, and 2) if a site doesn't include the xml file, I doubt any information could be retrieved.
So here's what happens today if I search for link:21cif.com:
Google: 48 results, many of which are from other 21cif.com pages
Yahoo: 1 result
From using other webmaster sites like majesticseo.com, where I had to create yet another account, I know there are 394 referring domains, 193 of which are educational and 16 are governmental. Too bad I can't see what they are without a paid subscription. This seriously impares one's ability to check the 'references' of a site by looking to see who voluntarily links to it.
Checking inbound links is not only of interest to a webmaster, it helps searchers be more critical consumers of information.
For investigative purposes, having a readily available link: operator has become a staple. Now the challenge is: what is out there that can replace it? For the time being, I'm recommended going back to Google.