I can see this going a few ways.
In the Panglossian Best of all Possible Outcomes:
Google uses Motorola's brand as a way to combat the fragmentation/carriers delaying updates issues by ensuring that all Motorola phones can receive updates as soon as Google releases them. They treat Motorola as basically its own company, in terms of the hardware. Motorola's phones now run pretty much vanilla android and/or motoblur is folded into the vanilla gui. (or you know, gone completely...)
Google unlocks the bootloaders on the phones, and reassures all the other handset manufacturers that they have no intention of (and actually HAS no intention) of aggressively moving into the hardware market or vertically closing their systems ala Apple. Samsung and HTC are appeased, and rainbows burst forth across the globe.
In the Orwellian megaCorp outcome:
Google has bought Motorola in order to compete with Apple, but in doing so, becomes their competition by any other name. Google remains "open" in name only, continually cinching the OS tighter and tighter in the name of "simplicity" and a "better end-user experience."
Google also uses this move to launch themselves as hardware providers (the Nexus phones having been the litmus test.) While proclaiming that this is just to provide better vertical integration, Google pretends to appease Samsung and HTC only to pull the rug out from under the other companies by reserving certain OS features and/or updates for Moto phones. Microsoft sits in the background and laughs quietly as Google's sticky fingers disrupt Moto's ability to build the better mousetrap. Having ticked of the other OEMs, Google finds itself in a neverending spiral whereby they close more to compete with Apple, because they no longer have the broad hardware base that allowed them to be a viable alternative. Disillusioned users buy Grid phones and weep for the days of yore.
Mostly likely, there will be little bits of both of these outcomes, but as for me, I'm always hoping for rainbows and preparing for doublespeak.
