John Moltz had an interesting take on the topic of in-app purchases, summed up nicely by these quotes:
Well, sure. Ask a heroin addict and they’ll probably tell you the same. In-app purchases are just like the proverbial drug pusher, giving the first go round away for free in order to get you hooked with each subsequent high giving the promise of an even better one the next time.
What we should be asking is simply whether or not we’re spending what the app is worth. We’ve spent a lot of time decrying the race to the bottom in app pricing. Now we’re complaining because app developers have found a way to make more money.
I've previously written about in-app purchases and the culture of freemium and how both are hurting modern video game design (as well as apps in general). To be fair, I do think that there ways that in-app purchases can be designed in a way that isn't abusive towards users.
In his post, Moltz gives a fair assessment of in-app purchases. While they are often disdainful, in-app purchases are not inherently evil. He is correct when he makes the comparison to drugs and gambling. People with addictive personalities will be easy prey for exploitive tactics, while others will not be directly impacted much at all.
Folks, be mindful of the difference between good and bad in-app purchases (developers, this includes you too).