I'm not an engineer, but I can tell you what I lot of my friends have done in internships and co-ops. It is harder to get such an opportunity as a freshman or sophomore, but definitely worth while, the sooner the better. Juniors, seniors, and grad students usually get accepted into most internship programs.
A friend of mine got a co-op position at United Space Alliance her sophomore year. She primarily worked on paperwork for the Space Shuttle. She learned that engineering wasn't what she wanted to do with her life, and dropped out.
My NASA internship this summer was primarily for engineers (who never brought their bosses coffee). They were essentially employees for the summer, working on real projects such as designing composite materials, testing materials, designing instruments for a mission to Mars, artificial intelligence research, propulsion, and other things I don't much understand. All of them were either seniors or early grad students.
None of those are computer or electrical projects, but I listed them just to give you an idea. As a side note, all of the above were paid (some are volunteer-only).
In my opinion, internships are very valuable because they provide you with real experience in your field. You can discover what you like and what you don't like. You'll also make contacts in your field, which can be very important to your career. Take advantage of internship opportunities if you can.
