Berkeman, if you don't know what A levels are how can you expect a young dude from the UK to know what AP aclasses are? I'm old dude from the UK and have no idea what AP classes are! The advice to "take all the calculus, physics, and electronics classes you can" is confusing. You *have to* take A levels maths and physics, and all the "calculus, physics and electronics" you need to take is contained within those two A levels.
There is no such thing as "a general engineering/physics track". In the UK and you need to decide which way to go while taking your A levels. In your 3rd year at College in the UK you are finishing your BSc degree! That said, you make a good point when you say:
"There really is is a lot to be said for looking around at subjects in technical depth, to see what really excites you."
But in the UK you have to (try to) do this when still at school.
I just re-read C.P. Snow's excellent "Two Cultures" essay and he makes an excellent comparison between the US and UK systems. Shame on both, actually, for not fixing any of the faults in either system in 50 years!
Robousy - these are good questions to ask oneself, UK guys just need grow up fast and start asking them good and early!