Pinterest and yes, I've found it quite similar to Image Spark. Except for the simple fact that it is public. I do like that you can add other uses to have access to pin your boards - allowing for collaboration.
Now I'm too sure how I'll go about using my boards - will I use them to catalogue my interests, share blog posts I've written, share pictures I took with Instagram or just compile things that inspire my work.
If you'd like to follow me on Pinterest you can so at www.pinterest.com/nictatt