I don't date, so I can't speak from first-person experience.

This isn't the most common issue, but a complaint I've heard that still tumbles around in my head was how few men on the dating scene were into reading books.

Probably the most common issue I hear from others is that all the "good ones" were taken and there are no good single people left to date.

I hear this from both men and women, and it's usually from people in a >25 age range, i.e. ages when most people have already paired up and married and had kids, so the dating pool is either full of "discards" (people who failed to find someone to pair up with at the "appropriate age") or people with a history of failed relationships - in general, the available people are all the people who are not promising relationship material because the "good ones" are already taken.