Its frustrating as hell, yes. I also find it flattering in a vein kind of way, but also I don't let it stop my being creative. Photography is a huge huge passion of mine but the potential issue of Copyright infringement I don't let that stop me. Ultimately, compared to the amount of images I've put online the amount that have been copied is very very small (maybe that says something about my photos? hehe)
I get a kick out of photos, when I get 'the' shot it gives me a real buzz. If someone wants to try and take a copy of it? Bring it on.