I like doing all sorts of scrapbook challenges, although I have not had a lot of time for them lately. Like Cassel says, they can stretch your ability or jumpstart a page. I also like to learn to make my own things, and if that could be included in open forum kind of challenges, that would be great.
Doing a challenge, and seeing how others treat the same challenge, may help increase your confidence. Even if you aren’t confident enough to post it this time, you may with a bit of practice. If you aren’t sure about something, you can put it out there, and someone else may pop in and give you some gentle pointers. Feedback is always a HUGE learning tool. Sometimes I have trouble finding how to do a step, like the gradient in the Reflections Tutorial. I was happy with what I achieved, but I would accept and appreciate anyone telling me where I went wrong. I also love to look at other people’s pages for inspiration for my own book.