20% is really huge in such a short timespan. Chrome must be becoming increasingly one of the prominent sources of user data for Google.
I don't think so. I am surprised it isn't higher.
First of all, Chrome's advertising campaign is immense. Chrome ads are plastered all over the web, including crucial places like google.com. Chrome is spending more on advertising than other browsers have available altogether.
Second, Chrome is a good product. Google has invested enormous resources into it, the kind that only an industry giant like Google, Apple and Microsoft can do, and the results are exactly as you would expect - good.
Third, we are also starting to see some special integration between Google web properties and Chrome, optimizations that appear only in that combination of browser+website. (Even if these are not proprietary protocols and so forth, Google still has an incredible advantage in the direct connection between the teams.) Leveraging Google's websites like that is a special advantage of Google that other browser makers do not have.
In summary, for these three reasons, I don't think Chrome's market share is surprising at all. In fact I am surprised it isn't higher.
They're even in meatspace. There have been Chrome ads in Paris's métro since early 2010, and they were still going strong last time I went there (a week ago), although they're only in a few places now (during the early part of the campaign, Chrome ads took over whole stations)
Clearly, Google made headway on these issues, but I think you underestimate how profound consumers needed (and still need) to be educated that they even have a choice of web browsers and that choice impacts their daily web experience.