Techcrunch has a good summary of the unique visitors to each of Google’s services comparing this November to last. It appears that Maps, by Comscore’s measurement, has 17% as many unique users as Google Web Search has. This % is significantly higher than last year.
Greg Sterling has a good analysis of the numbers. However given that Google Maps data is pushed out over a number of different technologies, the Comscore count may be underestimating the number of unique users of the data set and the overall usage of Maps. Those technologies include Google SMS, Goog-411 and Google Maps for Mobile. The extent to which users of Google Maps is undercounted is unclear but it strikes me that the undercount is greater on Maps than any other Google property as it uses more distribution technolgoies than other Google products. Regardless the number of unique users of Maps is starting to take off.