Hi Leeder
I wouldn't add brambles to the compost no matter how small you chop them. I have two dalek bins from the council, and added brambles a few years back, still trying to get them out of the compost and the garden! The bins just don't get hot enough.
Perennial weeds such as docks and dandelions I would definately not add - again, I'm plagued with them both now! Not sure about nettles, as I don't have those... yet!

__________________
Cheers
Marion
--------------------------------------------
A smile costs nothing but gives much
Gardening requires a lot of water... most of it in the form of perspiration.