what are amateurs actually doing?

hi,

short introduction: I am about to pick up my astronomy hobby again (left it
about 15 years ago, when I went to university to study math). Hopefully my
scope will be here within a week, and I am really looking forward to it:
stugying mars of course, but in general, I look forward to a winter full of
dark crisp skies.

I have a phd in math, but I am not a science professional (left university
after I got my phd, now I work for a large bank). I enjoy my current work
very much, but I never lost my interest in science (in fact, I published an
article on chromosome structures, together with my twin brother, in
"Science" last year). I enjoy astronomy as a hobby as it is abstract and so
close to real science.

My question: are amateur astronomers actually contributing to science
(besides shooting nice images!), and if so, how? Perhaps a FAQ, but I am
interested, as I know from experience, that my hobbies tend to get pretty
serious over time :-)