Peter Cohen of The Loop has a few comments on the whole "Google has bought Sparrow" situation, referring to a smart article by Marco Tabini. Unfortunately there's one point in Tabini's piece that I believe ignores the reality of buying software licences.
I encourage you to read both posts. My take on the situation can be found below and in the comments of the article on The Loop.
I can get behind most of what Tabini wrote in his article, but not the quoted passage. In it he warps what he calls "the simple reality of commerce". By definition customers who buy your products are stakeholders, they take a chance with your product and thus a stake in your business. This especially holds true for licensable goods like software as they are durables and not consumables like, say, toilet paper (here your business relationship and expectation ends once you've wiped you butt with it).
Tabini says that you should buy software that suits your needs, not because you have some hopes about its future, yet when a person invests in software by form of a licence, they expect to get a certain use out of it that extends beyond using it once or twice. Buying and using software is more akin to a service relationship than to buying physical goods.
Now to be perfectly clear: I don't expect developers to support a piece of software indefinitely — not for free at least. The question of "How long is long enough?" leads to a wholly different world of pain, but as JimD has correctly pointed out, OS updates do tend to break software and Sparrow for the Mac and iOS haven't been on the market for very long.
The same holds true for Pulp for the iPad by Acrylic Software, an app that hasn't been around very long either and that I bought — yup, my fucking luck — three hours before the announcement of the acquisition by Facebook. After purchasing the app, I found out that certain essential aspects of the software didn't work as advertised, something I'd expect the developer to improve on. Now that they've been purchased none of this will happen and I basically have a dud sitting on my iPad.