I applied via StackOverflow job advert. After sending my CV I was assigned a home assignment: a small iOS app. The assignment was defined precisely and it was quite interesting to me. I've finished it on the weekend (3-4 hours in total). The response was quite positive - I've qualified to the next round. Then there was a silence.... 2 months later I've sent them an email and the replied "sorry" but they had found someone interesting already. So, not very professional but I think the reason was a large number of candidates.