They either become software engineers or corporate types
(Wall street or consulting).
There are occasional rumours of physicists continuting to do physics after
graduation, but there are considered to be academic legends (like
bug-free code is to CS types).
By the way, I found:
My only attempt a lay physics was in explaining how rubber balls scatter off
a racquetball racquiet, and I got it completely wrong. (Although I did
figure out the Levitron [see earlier FoRK post]).
-- Ernie P.