The Chrome team has already published documentation outlining general goals and principles for how they believe the extension system should operate. High on the list of reasons that adding extensions to Chrome is important is that it will make the browser more attractive to “users coming from other browsers who are used to certain extensions that they can't live without.”
While extensions will certainly make the browser more attractive to a certain subset of users, the bigger fish to fry for Google is adding a Mac version. That too is in the works (see documentation here), but if Chrome wants to draw in a lot more users of its browser, Mac support will be key, as these users have so far been completely shutout of experiencing the benefits of Chrome.
As for how Chrome is doing so far, in addition to their self-reported 10 million downloads, our internal numbers show that Chrome is currently used by 4.50% of our visitors, up from 4.00% in the previous 30 days. Those numbers are no doubt higher than the general population given our tech focus, but point to a slight uptick in Chrome adoption.
Additional Resources from Mashable