Google recently added the ability to write on a mobile device screen with the finger to input search terms in the web browser. The Handwrite option is fully integrated into the browser search, including Instant Search. Start writing a search term on the screen and Google starts returning results, no keyboard required.
Handwriting recognition has long been the domain of Microsoft Windows, beginning with the largely failed Tablet PC. Good recognition accuracy depended on the special pens used by the tablets for precision. The introduction of Handwrite by Google is a foray into this territory formerly belonging to Windows.
Google Handwrite is pretty accurate in testing, although anything longer than simple search terms is not practical. Search by handwriting must be enabled in the Google search settings by visiting google.com, and then enabled on a case-by-case basis by tapping the "ink" button on the screen.
The handwriting recognition has shown to be accurate and fast when used on the larger screen of the Nexus 7. It also works well on iOS and Android phones. While on the surface it seems to be a gimick, in practice it is already showing to be practical and useful on mobile devices.
The timing of the appearance of Google Handwrite is probably not by accident. Google is making a statement that ink input is useful for limited purposes, and more importantly that it is cross-platform. You don't need an OS that supports inking, you can do it on both iOS and Android, the two big mobile platforms. No Windows required.