The number of search results is plenty useful. Even for grammar! If spell checker isn't of help, use Google and see which option is more popular (I used to use it often when I wrote more in my native language, which has a few peculiarities). It can give valuable insight in popularity of different things.

I do hold the number of results trustworthy (not exact, but a good estimate). Having the index in the Inverted Index format, and efficient joins (solved problem), it's just about getting the size of the term list and summing over the shards. Something that Google anyway has to do for the regular retrieval.