Being a Canuck, I'm a little unsure of what an intern actually does (okay, well I know what some interns do...). Is an intern just a student working for the summer, or someone who has graduated and is looking for entry-level experience?
My planning education involved a co-operative work program, where I would be placed with employers for four month workterms. It operated somewhat like the real world - we had to be interviewed, etc. And we got paid - helped with the tuition and beer money. But anyway - to answer your question, some experiences were better than others - I had workterms where I was copyboy, computer fixer-upper, and general gopher - and others where I was given a great deal of responsibility (relatively speaking). I think your experience is shaped greatly by who you work for - if your employer is interested in you as a person, or just wants somebody to use to do all the menial stuff they don't have time for.
Now that I'm the one hiring interns/students (well, at least in my two previous jobs), I definitely try to get them involved in everything - and to an extent, that is shaped by their interest. If they really want to be a planner and show some enthusiasm, they get to do some really cool stuff (cool being a relative term in the planning world). If they just sit there, they don't get so much out of it. And they learn how to use the photocopier real good.
A success story: One of my interns just got hired into the job I left. I like to think that the fact I gave her some good experience had something to do with it.
No intern jokes, please.