The core of my disappointment is the expectation of future development that comes with buying into a relatively new piece of software. I didn't buy Sparrow thinking I was paying for a piece of software that was feature-complete. I bought Sparrow mail as a piece of innovative software along with the promise of lots of great future updates to come.
Now, those future updates are done, because Google killed them by acquihiring the Sparrow team.
It feels like more and more, when buying into a new exciting project, the risk is less that the project will fail on its own, and more that it'll be destroyed by an acquihire. Some day, I wouldn't be surprised if this becomes a barrier to startups acquiring dedicated new users.