Google’s bonus was not the usual this year. Upsetting to the CTO maybe.

Mr. Horowitz wanted to transfer to another area and was rebuffed, upset with the Android direction, upset with fellow co-workers, upset with Google’s direction. Basically some form of corporate politics.

Coupons.com can’t have dangled money, it is likely this guy has “enough” but maybe the equity stake was to good to pass up.

And my last most plausible option:

With his pedigree and capital it is likely he invests some of his money/time (sweat equity) in a number of ventures either independently or as part of a VC/Angel firm. It is possible that this firm requested or he saw this company “needing” his guiding hand.

@Rob – I hope you do keep tabs on him and let us know what you find out in the coming months. Maybe you could score an interview with him.

OR: his salary at Google was no good ;)