Sorry for the delay - we just got this sorted with Vimeo.
First of all, they have been absolute peaches to work with. They are great, and not unreasonable at all. Our use was VERY high - we're running feature films, and have a library of approximately 2000 films, and running 5 channels. The cost per GB was reasonable (flat fee based on average use per month) - cheaper than S3 and a lot of other players out there, but more expensive than we could source elsewhere. Since our content is ad supported, we're pushing pennies across the table, and small differences are important, so we'll be hosting elsewhere. We came up with a plan to transition off of Vimeo in an agreed upon timeframe to transition our traffic off of their system. We're still going to keep the Pro membership as a backup, should our new CDN experience a server failure/outage, and Vimeo was fine with that. I want to stress that they've been VERY reasonable to work with. They stated on several occasions that they're not interested in shutting us off suddenly, or holding our feet to the fire - and they were good to their word.
One of my channels currently streams about 6TB of data per month and was considering switching to VimeoPro. Does anyone use Vimeo that transmits this much data and if so, did they charge you anything extra?
From Vimeo Pro FAQ: You’ll never encounter surprise charges for overages, so long as you’re using our gorgeous player.
Yep - you'll get an email. But, depending on your CDN, it may be a decent deal, particularly given the convenience of the Dropbox API, and their automatic transcoding, and the ease of using their playlists. They also limit the number of API calls per hour, so using them will depend upon how much activity you have. I'd rather not post specifics publicly, as I don't know what their costs are, or what cost range they're offering users. If you have more detailed questions, feel free to PM me.