My guess right now is that Google will start to catch up in the tablet computer space when Android 4.0 ("Ice Cream Sandwich") ships around November 2011..
This assumes that Apple is "sitting on their hands" when it comes to developing iOS, iPad hardware, and the iPad ecosystem. They aren't.
The fact of the matter is, Google will be very lucky if they are able to hold on to the roughly 50%
smartphone marketshare they have right now. And they'll be doing everything they can to fight that battle (where at least the road to profitability is feasible) - rather than throwing hundreds of millions into Tablet operating system development, where the profits are going to be a lot harder to come by.
How so? Most consumers have shown a preference for Wi-Fi only, or at least limited 3G and 4G access on their tablet purchases. This makes some sense - relatively few people want
another monthly data expense. The Tablet market has also shown the importance of Apps. Relatively few apps = not much interest among the wider consumer market. But an App-based environment means
even less opportunity for Google to make money. If the only way you plan on making money is by selling display ads - Tablets are a very bad way to go.
Google might hope to somehow leverage its purchase of Motorola Mobility in such a way as to create some form of vertical integration in the Tablet market. But actual physical products of that integration are probably at least 9 months away from store shelves. And they've also got to worry about keeping Google's other Android-Tablet partners happy in the meantime, or risk alienating them by showing preference to Motorola.
Its a very complicated game going on right now. Its not - in any way - a two-party "game of chess", with Apple and Google taking turns trying to outflank each other. Its more like a weird form of poker: Samsung, Lenovo, Acer, HTC, and RIM are all playing Texas Hold 'em. Apple is playing 7-card draw, holding a couple of Aces and two wild cards. HP just folded. Google just went All-In by buying MMI. Oracle and Microsoft just caught a few players cheating, and are holding out for a share of their winnings. Apple has accused some players of cheating - and hope to get them thrown out of the casino (if not actually hanged from the nearest tree.)