Yarp.
I like contributing to a community that I enjoy and that's all that matters to me, so I don't mind it if a fan does it, but I feel it's a bit different if a company/business/etc., does it. Then it's just unprofessional.
I do a lot of concert photography. It's all amateur/unpaid and for fans only for the most part. It's a hobby of mine. I enjoy receiving letters back from fans that are thankful for my pictures because they could not attend a show and they feel my pictures capture the concert going experience. That is fulfilling to me. But it is a bit disappointing to see my pictures chopped up, badly edited and floating around uncredited on the internet, especially that goddamn tumblr. I don't mind people using my stuff and I'm pretty open to it being borrowed. I just don't want it altered. But I rarely confront the individual about it, I'll just post a general notice that some credit would be nice. But when it's a major blog, news site, etc. using my work, I make damn sure there's a credit underneath that photo. But the majority of people that use my photos do credit/ask/etc., so I try not to let a few bad incidents spoil everything. But then again, I'm not getting paid, so maybe it just doesn't bother me as much.