It's a pretty large sample for qualitative research, actually. When you're building an app, a good way to spot problems is to run a user experience test. Sit d

It's a pretty large sample for qualitative research, actually. When you're building an app, a good way to spot problems is to run a user experience test. Sit down at the side of random potential users for half an hour each. Observe how they're using the product, and let them walk you through what they were thinking when you find it interesting. Past a certain number of users, major UI problems will surface again and again from test to test, alongside marginal - and arguably less important - tidbits of information that let you identify new UI issues. When you reach that stage you know you should stop. It kicks in at around a half dozen users in my experience - and is very rarely over a dozen.