The behavior of the site: operator has changed in the last two days. Previously I'd often issue queries including 'site:wikipedia' and results would include hits from wikipedia.org. Today when I include 'site:wikipedia' in a query I receive no hits. Using 'site:wikipedia.org' works as expected.

Note that you can still use something like "inurl:Wikipedia" along with a search term to get results like you used to.

<<results would include hits from wikipedia.org>>
A trick I worked out, type your keyword followed by "wiki" and the top result is likely to be wikipedia (I've only had one where it wasn't and it was the second result instead)

I still get lots of Wikipedia results for [site:wikipedia]. Maybe a datacenter thingie tho...

'site:wikipedia' is working as I'm used to again, getting hits including those at wikipedia.org. Strange.