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.