One of my favorite magazines, and one of the only ones I subscribe to, is The Sun. It's an ad-free publication of interviews, short stories, poems, and reader-submitted material that tends to engage the human experience in really amazing ways. It's sort of a hidden treasure in the world of magazines - either people tend to love it, or have never heard of it. They have a section every month called "Readers Write," where they pick a theme and ask readers to submit personal stories and experiences that relate to that theme.
Almost every month, I see the list of themes and think about what I would write about. I start to compose the words in my head. And then I look at the submission deadline for that topic (usually just weeks away) and then at the publication target for accepted pieces (usually many months away), and I tell myself that I'll come back to it later to actually send something in.
I've been a subscriber of the Sun since 1999, and I have not yet gotten around to submitting anything to them. I'm not sure if it's because I can't experience the instant gratification of having my writing accepted (or rejected) like I can with a weblog. Or maybe it's because I still have such a hard time letting myself write about things that other people are writing about. Or maybe it's because I know I would be submitting something for someone else to judge or value, and I'm not confident or vulnerable enough. Or maybe it's pure laziness, apathy.
Whatever it is, it's a form of writer's block that seems ridiculous and intimidating to me, yet very important to overcome.