I've been calling myself progressive since I was in highschool
Though at that time, it had more to do with my taste in music than with politics. I certainly do consider myself progressive (adjective). But I would fear calling myself a progressive (noun) because that would make me a member of some group whose characteristics are defined either by members of that group or by you. You certainly have negative feelings about the word!
In my case, it means an openness to new ideas. A willingness to try things out. An urge to examine how to make things better and to do so.
And PS: my definition of the word has not ever changed.