You can get struck by lightning easier than you can get HIV by oral. Note that the CDC claims that no case of HIV has ever been varifiably linked to oral sex - also note they still say it is possible.

Gonorrhea is another story. Chances are low for male recieivng oral, higher for women giving oral to an infected male. In both cases, still relatively low risk, but not unheard of.

you'll find pages of information, including some study results from different sources, on what STD's can be contracted by what activities. The risk factor is entirely up to your individual comfort level. I could go out today, and get run over by a bus, but I'm not going to stay home due to a remote risk of danger. By the same logic, I couldn't imagine seeing some of the ladies I've seen, without eating some pussy. I always play safe, within my own comfort zone, and respect the comfort zone of the ladies I'm playing with.