> Basically it means "Activate this profile unless the value is true" isn't?

Yes, right.

> I wonder if we should add a comment as a reminder. for when we use exclamation marks

Hmm, not sure. It's basically the normal Maven property syntax. As you say I think it'd be some kind of overhead. 

Btw. I'm absolutely with you in disliking this kind of double negation (a variable with a "negative" name such as _disabled_, _skip_ which then is negated) but I think there is no way around it here.