VLANs

Are any of you operators utilizing VLANs to/with your transit providers in order to isolate traffic types or services, and/or to assist in traffic shaping before it hits your transit connections (isolating the effects of DDoS's)? Would you be prepared to share experiences, do's/don'ts, gotcha's etc? Off-line responses would be fine, obviously - I don't want to add to any of the current noise.