I don't think there's any one silver bullet that's going to take them by surprise. For search I think the biggest danger is not being able to keep up with spamm

I don't think there's any one silver bullet that's going to take them by surprise. For search I think the biggest danger is not being able to keep up with spammers and tricksters. People may not abandon Google search but it would make their advertising platform far less appealing and open the door to competitors. For everything else there's the privacy & reliability concerns. A few big high profile privacy breaches, some frequent outages, or any hint of corruption in how Google handles personal data would take their toll. Purely on competition I think Google Docs is a weak spot. IMO it's pretty bad and has not been improving. Microsoft's Office Online looks pretty good. As inept as Microsoft is it would be unwise for Google to let them get a foot in the door. They might end up regretting the years they decided not to make any significant improvements to Google Docs.