I've never had writer's block, but sometimes I get a little bogged down and lose my enthusiasm part way through. I've learned that's not writer's block, though. Every time that's happened, it's because there's something in what I've written that isn't working... and my subconscious won't let me move forward until it's fixed. The tricky part is figuring out what the problem is - characters, plot, or some detail that I haven't even realized I've missed. As soon as I figure that out, I'm off and running again.