I had heard that they wouldn't do it after 6 months, and have had some friends really disappointed that they couldn't get their children vaccinated who are prone to getting every bug under the sun.
The problem with rotavirus (and the reason they only offer it to under-six-month-olds) is that you only ever get it once, and after that you are immune; and that after the age of six months, it doesn't cause the same kind of severe dehydration as it does in little babies. So it's a bit of a "one-shot-wonder", so to speak.

Given how contagious it is, though, if you're unlucky enough to have an under-six-month-old in daycare, I'd definitely recommend getting it.