I've recently asked a few questions about author identifiers for scientists (https://web.archive.org/web/20150922174131/http://network.nature.com/people/mfenner/blog/2009/04/13/a-few-questions-about-author-identifiers?). Here are the results (based on 48 responses). The results are also available as .xls file (https://web.archive.org/web/20150922174131/http://spreadsheets.google.com/pub?key=rpPHC7BnyO2VJPglm246fKA&output=xls?).