[india]

Oh this is what that is! I accidentally reach this mode now and then and wonder how I got there and what it does. I must be accidentally pressing q: instead of :q ! This is great and useful. Thanks!

[wmwong]

Same here. You can also do q/ which gives you the history of your searches.

[pyre]

You can get to search history mode this way too. E.g.:

  q/ - Search string history
  q: - Ex cmdline history
  q? - Search string history

Also note that if you normally use Ctrl-C to exit Insert mode, that fails here as Ctrl-C will close the history buffer. You need to use Escape or Ctrl-[.

[antidoh]

That's exactly how I found it, by accident. I think a lot of people do.