Studies to date on circumcision and hiv transmission have been mostly if not all done in Africa, and specifically on the penile-vaginal route of HIV transmission.
For pretty extensive bibliography, see:
http://www.cirp.org/library/disease/HIV/
http://www.cdc.gov/hiv/resources/fac...rcumcision.htm
Obviously circumcision is not going to be correlate to HIV infection via receptive unprotected penile-anal intercourse but would be correlate otherwise.
Another interesting observation I have made, after long, intense and close-up inspection of the Thai penis, is that there seems to be a high incidence of frenulum breve or phimosis. But I live in America where there are not (sadly) very many uncut guys, so perhaps my sample statistics is skewed.