Agreed. That's why I won't ride MUPs - I'm impatient and like to ride fast, so I'd be tempted to be the person you described. Instead, I stay on the road where speed isn't an issue.

For the occasions I'm able to curb my impatience, though, there are sore really excellent MUPs in my area. But they're so heavily used - especially on weekends - that you can't do much more than 10 mph.