In the past 3 years we have used points for :

Spring break in London
Spring break in the Carribean
Thanksgiving in Hawaii
Thanksgiving in the Carribean
Valentine's Day in New York City

I'm sure there are more high demand dates, but we've had some fabulous family/couple time at Marriotts when we wanted to.

As for high redemption rates- not sure what this means, except for upgraded rooms there is no fluxuating redemption rate at Marriott.