I've had three different museum internships, only one of which involved "dirty"
work, and after complaining about it, the second half of that particular
internship was quite rewarding.  I started off working in collections and
progressed to curatorial work, which I realized (because of the direct
experience of my internships) was what I was most interested in doing in
museums.   One of my internships ended up turning into a part-time position,
then into the current full-time position I hold right now.  Another of my
internships involved doing a substantial amount of writing for a major
exhibition catalog.  Defineitely staff level experience!

Granted, all three of my internships were completed in conjunction with degree
programs and were (gasp) *paid* internships.  Both the token salary and course
credit encouraged both my employers and myself to make these internships
rewarding experiences.

I know of many other interns who have had in depth, professional experiences,
though this may be unique to the particular fields of collections and
curatorial work (though I also know quite a few conservation interns who are
absolutely thrilled by their internships).

On the down side, I also know quite a few interns in more paperwork oriented
departments who ended up doing a lot of filing, mailing, and phone-calling.

Hope this was helpful,
Anna Friedman