Google said in July that it would be adding JotSpot to Google Apps, so this doesn't come as much of a surprise. The Google Operating System blog speculates that the launch will be timed with an announcement at this weekend's Office 2.0 event in San Francisco.
Last week, Richard MacManus wrote that the core products of a web office suite, are email, calendar, word processing, spreadsheets and presentation. Google, which this year acquired two companies working on presentation apps, will soon offer a suite that has all of those components. By adding wiki support to Google Apps, the company will be extending their web office with a product that could only be delivered on the web (remember, Richard's web office definition said that an online office package must extend "the functionality of desktop office suites ... by using Web Native features.")
Certainly Google Apps is not as comprehensive as Zoho's suite, but adding wikis and presentations will put it on firm footing in the web office wars and extends it into areas that Microsoft Office does not tread.