Facebook has announced a "modern" messaging system that will integrate email, text messaging, and Facebook messaging. Google's dominance, all of a sudden, is being challenged simultaneously on multiple fronts. And behind the scenes, it is often Microsoft that is leading the charge. Facebook's email service will draw some users away from Gmail, and Facebook has already announced a partnership with Microsoft to use Microsoft's Bing search engine for social search. And Yahoo! recently announced a plan to move to using Bing to power Yahoo!'s search services. Meanwhile, Apple is not standing still, with it's Ping music-oriented social network pushing both Google and Facebook. And Apple has some big plans that are still largely under wraps to challenge Google's Gdoc services.
If Apple and Facebook can provide better and more believable privacy policies than Google, which basically has the attitude that all your personal data belongs to them (check the EULA for Gdocs, which gives them a license for everything you create using Gdocs), the two firms will slowly chip away at Google's dominance.