this article by Carina really got me thinking about Pinterest, and this post today from Marianne at the Quilting Edge asks for other people's thoughts on it. You might find it interesting to read the article that Carina quotes in her blog, which you can find here.
It's certainly made me think, and I'm ashamed that it had not occurred to me to think of my Pins as anything other than handy links back to the original source. And like Marianne, I think I would like to know in the (unlikely) event that any image of mine was "out there".
Pinterest now offers a bit of code that you can install on your website which means that your images can't be pinned. If you go to the Pinterest help page here and scroll down to the part called "Linking to your Blog or Website", you will find an article titled "What if I Don't Want Images from My Site to be Pinned?". Click here and you will find a bit of HTML which you can copy.
In Blogger, which I use, you can click on the tab "Design" and then have a tab with the option to "Edit HTML" of your blog. If you click on "Edit HTML", you can look at the code. Scroll down to the bit which begins <head> and paste in your copied HTML just below. Save this change. Now go back to your blog, and try pinning an image. You should get a pop up box which reads "This site doesn't allow pinning to Pinterest. Please contact the owner with any questions. Thanks for visiting!"
[Added April 2012: Since Pinterest have made some changes I've felt a lot happier about some of the copyright issues and about using Pinterest - especially where bloggers are making it clear with the Pin It button that they're also happy with it.]