Any reason why you ask this question? I've often been wondering about this myself.
In an effort to enhance fuel economy, stay high longer, I've been limiting descent rates to no more than 1,000 FPM unitl intercepting VNAV glide path. Some have questioned this procedure (speaking from the USA system).
After querrying various US ATC facilities, the general response I received was not less than 1,000 FPM for early descents. Most early descents are the result of LOA between center sectors and are not traffic-conflict related.
Has anyone heard othewise, speaking from a US airspace user's point of view?
Thanks