i did a free internship after working professionally for several years and at the time i turned down a paying job. my dad thought i was crazy but it was one of the best decisions i've made in my career. this was because i took an internship under the condition that i only work on certain technologies which i was banking would be big earners in the future. within 6 months they were paying me hourly for my work and then after another 6 months i was able to get a full time job working in this new technology where my salary was proabably 50-75% higher than it would have been if i had taken the paid job. also, i used to run a regional skateboard magazine and i had 4 design interns work for me. they did a great job, got good porfolio pieces out of it and i used my network connections to help them land jobs at companys where i had contacts plus helped them learn the tech side of web design (usability, etc...). they all seemed really pleased with what they got out of it.
but don't be a chump and have a shitty attitude about not getting paid. you don't get paid in school, infact you pay them. so just think about the fact that you are gettin more valuable knowledge without having to pay. find an internship that is in something you really want to do and then go in there and kill that shit. treat it the same way you would if you got on flow with a good company, they aren't paying you but you would still break yourself off for them.