I purchased Sparrow back when it was $9, and didn't find it particularly amazing. I did like it, but ended up using the web interface more. I certainly got my $9 of value out of it, though, even though I used it for a short time.
There's been a lot of complaining about Sparrow's acquisition, and a lot of complaining about complaining. Most of the complaining about the complaining argues that those who complain should feel like me: You bought it, you probably got a ton of value out of it. You can't (and shouldn't) complain.
Theoretically, a market works through feedback mechanisms. That's the whole 'free market' argument, right? People that participate in the market come together, the magic happens, and everything gets allocated correctly. Vote with your dollars. Shop somewhere else, and poof! A store that's too expensive won't be able to keep its doors open. A triumph for 'free commerce.'
So why does everyone get all huffy when certain people provide the market with feedback about the way that business has been conducted?