We have them alllllll the time. Plus every Tuesday is our corporate fast day until 6:00p (I never do those, though, because I can't seem to remember and get in the habit

).
My pastor calls a corporate fast at least 4-5 times a year, plus God calls me to my own fast from time to time. What sucks is when God calls me to fast first, and then speaks to my pastor next. That happened last year, when I was coming off a 40 day fast, the church was starting a 21 day fast. I think my last week overlapped with the corporate one, but still man...
That's why I gave myself a 7/7.5. I'm fine when it's my own fast, or the corporate extended fast. But I never do the weekly fasting on Tuesdays.