The Simple English Wiktionary is coming along quite nicely. We're at 1427 entries now. Though that doesn't seem like many, we only had just shy of 400 when I joined last April. My goal is to get a good basic vocabulary in there, about 2000-3000 words plus the Academic Word List. If anybody's interested in contributing, contact me ( b r e t t . r e y n o l d s @ h u m b e r . c a) or just head on over and have at it.
If you're interested in using the data to study vocabulary, there's an open-source program called jVLT that can import the data from the SEWikt for study and testing. I don't think the importing program has been uploaded yet, but I can send you the data if you're interested. Again, let me know.