I think recognizing talent in the context of an interview is difficult, but not impossibly so. I think judging how well they work, (do they 'get stuff done') is much more difficult during interviews, unless the person has solo projects. I know working for others, I've recommended several 'smart but useless' people after interviewing. Usually when hiring people I know, though, I know in what ways they are useless, and can hire for positions where I can make up for their weaknesses.

but I don't think it's difficult to judge a person if you have known them for a while, especially if you are the type to talk about technical things in social contexts.

I think the problem appears when you are judging things outside your field, or people you only see for an hour.