They wouldn't be surprised. I've always liked biology. I have barely changed at all since High School, in terms of my temperament. I suppose the only change they'd be surprised in is my shift towards Centrism on issues of foreign policy (I'm still on the left in regards to social issues). They'd also be surprised that I no longer dislike the US exclusively - I despise pretty much every nation now. They're all bad.
No they wouldn't be surprised at my career choice. If I told them what I was doing, they'd pretty much say "Yeah, I figured you'd go into that". I wouldn't rub my profession in anyone's face either - I got along with just about everyone. I wasn't popular by any means, but no one hated me. I was just "that guy" that no one knew much about or bothered to notice much. Which was pretty great. No pointless school yard drama, no bullying, no "social group" nonsense. I treated school like a job, and everyone around me was completely neutral in regards to me.
Hell, I wouldn't even go back to my highschool reunion. Didn't bother keeping in touch with anyone after I left.