Easy to use interface, comprehensive configuration options
1. There's some kind of glitch with mobile users on iOS when you're preferences aren't configured currently, people can't view your videos (and with half our traffic coming from iPhones and iPads, this was a HUGE problem). We had to go through hundreds of videos and manually re-configure them to work with iOS, crazy!
2. The service routinely goes down. Not like once or twice a year, but once or twice a month. This means your videos don't work. So all your paid traffic is going to broken pages with a video that doesn't play. Videos are critical to our advertising, and with them not working, we see a substantial dip in sales.
3. Their reporting is weak. For business use, we need too know average time people watch and other data points that aren't available in report.
Not sure why they have routine outages each month, sometimes lasting 5-10 mins (during critical business hours). There's never notice or an email explaining why, or how they are working to fix the problem.
We've since started replacing our Vimeo videos with YouTube, since it's more reliable for business needs.