Here is my rather personal answer. I like Wikipedia---both in general and the mathematically oriented part, and I would like to collaborate in its improvement and contribute in any way I can. But I don't know where to begin. With MO, when I have free time I can start "at the top" so to speak, and continue on down until I start seeing familiar entries---but in Wikipedia how does one decide what to look for that might benefit from one's inspection and possible editing. Getting over that intimidating problem is what prevents me from even getting started. I think it would help if "we" (i.e., the math community) could set up a website where there was listed mathematical subjects that either someone had spotted as being ignored by Wikipedia, or whose Wikipedia article had been recently edited, or which someone had read and felt would benefit from expansion or improvement. It would be good if such a site was maintained in chronological order by date of entry so one could view it from the top for new stuff as one had time to do so, and it should allow comments and "answers" to each entry to show any progress in fixing the problem. I guess some sort of "stack" is what I have in mind. I would certainly be willing to visit such a site frequently myself and contribute to it as I could.