googling "site:imdb.com ..." uses google's index, restricted to imdb.com; DDGing "!imdb ..." uses imdb's internal search.

I almost never bother with sites' internal searches, as google's "site:" feature almost invariably works better, so I wouldn't be inclined to use DDG's site-search bang-lines myself. YMMV, I guess it depends on how good the site in question's internal search functionality is.

Heh, I always use Google instead of most site's internal search engines. Have you ever tried using MSDN search before? Even with the advanced filter options, the results are awful, awful, awful compared to what Google pulls up.

See also the mind-bogglingly dreadful search provided by Amazon.

I dread to think how many human hours have been wasted because of sub-optimal Amazon searches.