Why wouldn't I "date" him? Let's be realistic, going to dinner with someone and going to the movies together isn't going to give you HIV.
Let's be blunt about it - what you mean is would I have sex with that person. And my answer is - why not, provided you take appropriate precautions against HIV transmission?
What bothers me about this question is the implication that if someone DOESN'T say they are HIV+ they must be negative - and also the suggestion that it's the other person's responsibility to protect YOU by telling you, someone he may have just met, about his health status when it's not even certain whether you will end up in the cot or not. I'm not saying that JohnnyF thinks that way, but I fear a lot of people do.
In some countries it's the law that you are responsible for your own protection, and I think that's the right attitude. You shouldn't be able to let someone fuck you without a condom, and then go round yelling "He infected me with HIV". Bullshit. You let the infection in. the only time the other should be held responsible is if it was a case of rape.
Sorry to rant about this, but I have been to a number of gay health awareness seminars, and I get the same message time and time again - most of the infections happen because guys who believe themselves to be negative take the attitude that the responsibility for protecting their own health all lies with the other person, and that in turn means that many positive guys don't discloses their status, because they fear rejection, or, worse, that the person they tell will then go and broadcast the information around town and on the Internet for everyone to see.