Version 1.0.1 - limitations

What are you trying to do with the CVTs, and what have you tried so far? They're absolutely accessible via MQL, but you'll probably have to make a more complex JSON structure to get at them.

Image paths and short descriptions aren't gettable directly in MQL. You have to take the ID number and then build a URL out of it, in both cases. I'm afraid I don't have the URL format right to hand at the moment, and am just about to head out the door, but you should be able to find some examples. It's like http://freebase.com/blah/blah/image/ or something. The same goes for the descriptions; the magic word is "blurb" and there was a recent thread on the dev list about them. Lemme check... yup, http://lists.freebase.com/pipermail/developers/2007-November/000939.html (and its responses) talks a bit about blurbs.

There is a cvt on wine called grape variety composition, and if I retrieve potential instances of it I only get empty fields (they need a combination of both grape variety and percentage).
IYou could retrieve that information if you know in advance that this is a cvt, but in my case I wish to build a generic application that interprets the type of property (boolean, datetime, integer, float, and other including ctv) and based on that allows you to input specific values, so I would not know in advance that a property is a compound value type.
There probably is a way of knowing whether it is or not, but I haven't found it out just yet, so any help is appreciated :)
I found some documentation on images and html content in chapter 4 of the documentation, so that is more or less resolved (still need to study it).

ontologyonline, I see that crism's answered a related question for you over here ... is that what you were looking for?