Gabe's posts have had strong impact on a relatively small audience. It's hard to realistically imagine it's had a significant impact on Surface sales one way or the other.

On the other hand when he blogs about the future direction that they are taking then this is all data that competitors will gobble up, and in many cases can bring to market ahead of MS.

Quite possibly the PR gain here is offset by the future opportunity cost by giving competitors a heads up on future strategy.