People spent an average of 10 minutes in October, and 14 minutes in December. "Users of Google Docs and Spreadsheets skew toward higher incomes, with 28 percent of users earning upwards of $100,000 annually. A large majority of users, 76 percent, have an income greater than $50,000 annually. Users of Google Docs and Spreadsheets are typical of technology early adopters. They tend to be mature with some disposable income. As more providers of Web-based productivity tools come to market and consumers become familiar with their offerings, we will see the audience broaden to more closely resemble the overall online population."
Also it's interesting to note that Google Docs & Spreadsheets doesn't have competition. In October 2006, 92 percent of the people who used Web-based productivity tools chose Google Docs, and not EditGrid, Zoho or Thinkfree, even though they have many interesting features and sometimes they are superior to Google's tools.
To compare these numbers, Gmail had 5,514,000 unique users in November 2006, according to the same company.