I met him because he was moderating the panel "Why Hard SF So Seldom Crosses Genres" or something like that. Peter was the perfect moderator because he's Mr. Hard SF— or in his case, Dr. Hard SF, as he in fact a scientist. He was also charming. a good moderator who kept things moving, and very kind to a programming newbie. He does have a quirky sense of humor; his idea of stirring things up was to announce that The Lord of the Rings was hard science fiction.
So how did this guy end up spending a night in jail and facing a fine and a 2-year prison sentence? Well, that's the question. The account in the Toronto Star does a balanced job of describing the event. Read that and come back.
Most of the US media seems to parrot the US Border Police's version of the story. The Twitterverse, however, has been humming about it and organizing support. The gang at Boing Boing, who pretty much broke the story, have pointed out that even in the best of circumstances, Peter will need help with his legal bills. If you feel moved to support him, the info on how to do that is available on the Boing Boing link above. Some folks have been buying his books; others (like me) have donated through PayPal.
If you want to know Peter's feelings on the matter, he has posted on his site about it. It's a good illustration of the principle that the one thing you don't want to do is piss off an eloquent person with a platform.