Followup on "IQ-boosting exercise": Cognitivefun, my website for cognitive exercises

I have been working on a general purpose site for cognitive tests, for informational purposes and out of interest. It's also the first thing I thought of doing after learning some Flash.

One of the tests I decided to include initially is an n-back task variant; as per http://news.ycombinator.com/item?id=176264 , NewScientist wrote about a recent publication using an n-back task, so I thought I should demo while it's still fresh in memory. Forgive its simplicity (and again, it is a variant), but as always, I'd love to hear your feedback.

http://cognitivefun.net