In the past, we provided users with the “+” operator to help you search for specific terms. However, we found that users typed the “+” operator in less than half a percent of all searches, and two thirds of the time, it was used incorrectly. A couple of weeks ago we removed the “+” operator, encouraging the use of the double quotes, which are more likely to be used correctly.
that may have had something to do with it, but i think you can probably trust the official sources that it really wasn't used much and was often used incorrectly. i've met more than a few old people who had been told at some point that they always needed to put plus signs between words instead of spaces, no matter what.
Actually, Google decided to repurpose the + operator for Google Plus Pages Direct Connect (http://www.google.com/support/plus/bin/answer.py?hl=en&p...).