I looked in the logs on my public web server I host different sites on. I only found one UIDH record in my modsec_audit logs, but most worryingly it was it was for a personal injury trial lawyer. Made some records semi-anonymous.

--eee7b544-A-- [25/Sep/2014:15:33:19 --0500] VCR8D6wUChkAAG-HuKQAAAAH 70.209.73.XXX 32675 X.X.X.X 80 --eee7b544-B-- GET /wp-content/uploads/2012/07/XXXXXXXXXXX.jpg HTTP/1.1 X-UIDH: MTU4NTI5Mjg3AKafKcbQqnDdCMuP+UbmoCyKvEu8MnDsqV0I+AQ2K/M+ User-Agent: Mozilla/5.0 (Linux; Android 4.4.4; XT1030 Build/SU4.21) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/33.0.0.0 Mobile Safari/537.36 GSA/3.4.16.1149292.arm Host: www.XXXXXXXXX.com Connection: Keep-Alive Accept-Encoding: gzip