I really love the idea of spaced repetition, and I really love Wikipedia. I wish, however, that there was a fusion of the two spaces. Imagine surfing Wikipedia, reading an interesting fact you'd like to remember, and simply clicking a button next to it that added that fact to your daily spaced repetition learning database.

Also, while there are good spaced repetition programs/databases out there (like Anki), the databases aren't collaborative like a Wiki, and in general could be much better. Actually, collaborative abilities aside, I think even a very well kept but closed database could be quite valuable (more so than Rosetta Stone or other such software for learning a language for instance).

Tackling some of these ideas is something I'm planning on doing once I finish up my current projects, but if someone else jumps on them first, all the better.