I use these quite often, but not quite in the way you are hoping too.
I guess I use them in more traditional amounts. At around 5% they seem to contribute a nice smooth fullness or mouthfeel and also seem to help with head retention. At these amounts I don't really get any detectable flavor contribution.
I would guess that's how most people are using them. I have heard they can give of a berry type of flavor in larger amounts.