Both of the things you mention are directly work-related. Can you give some other examples of " things on the public Internet that reflects poorly on the candidate?"

For example, does posting something about anti-semitism reflect poorly on a candidate? How about a candidate that makes strong statements about the correlation between race and IQ?

Those kinds of social issues are relevant for two reasons.

1) If the candidate has to work on a team with others, then he has to get along with the team - or at the very least, the chemistry shouldn't be bad enough to affect performance.

2)I think it's perfectly acceptable to reject someone because you don't consider him to be morally upstanding. The second statement about correlating race and IQ is a bit ambiguous and subjective, but if, say the candidate was philosophically in favor of lynching and ethnic genocide, then I wouldn't care how good a hacker he is, I wouldn't feel right hiring him.

Posting race\IQ issue wouldn't, in my opinion, reflect poorly on the candidate even though I don't necessarily agree with it. On the other hand, posting anti-semitic remarks probably would reflect poorly, depending on how they were phrased and the context (is it just pure hate or mere opposition to certain political stances...)

Whether they reflect poorly or not is a matter of personal philosophy. If I was face with someone who was blatantly racist, it would reflect poorly on their suitability for a job where they to interact with people who would take offense to such views. For such things, a decision would depend on how negative I anticipated that interaction to be. This is no different from not hiring someone based on their poor social skills during an interview. It is in public and they must expect it to be scrutinized and associated with them.

Eh, I'd say you aren't being fair, no. Not that any interview process is really fair. I once worked with a guy who told me stories about waking up at work at his desk, not remembering how he got there. He never did anything remotely like that working with me. For 3 years he was sharp, punctual, and competent.

And frankly, the reason and manner in which someone left their last job is a piss-poor reason for not hiring someone. What if there was sexual harassment? Stuff like that you can't know from a google search or even an interview.

As an employer, I reserve the right to use any public data obtained from web/Usenet searches to understand where a candidate is coming from in his/her professional life. It's basic due diligence, whether legal or ethical or not, and I expect prospective co-workers to do the same to me. Moral: don't be a dick or a moron online, at least not in connection with your real name.

That said, the real peril is that of mistaken identity. I almost missed out on a (mostly) enjoyable 2+ year relationship because my Google search revealed that the woman I was chatting with was an activist for various evangelical Christian causes. Fortunately, before breaking contact with her, I asked her about it, and soon realized that Google was leading me astray.