While having access at all is nice, the terms of use are prohibitive and somewhat heavy handed. They basically say you can make something, but can't charge for it in any way, you can't create a mash-up (no augmentation of data) and if it works out, Marvel will probably implement it for themselves anyway. Not really as 'open' as you might hope. The following default rules apply to all Apps: Advertising. No advertising…
That's from Google's TOS [1], which applies to GMail. So Google can, in theory, publicly display your email.
I guess that's my way of saying that I'm much more interested in the fact this API is available for exploration and experimentation and much less interested that it doesn't meet an impossible standard that no one here can actually articulate or provide an example of.