Simon suggests some sort of integration between plantemath.org and Nupedia/Wikipedia.
All three projects are GFDL'd, so collaboration is easy (planetmath requires no invariant sections). No work is ever lost. I don't see a need for tight integration, and as Simon pointed out, the projects differ in several respects. Whatever good content they produce at planetmath we will use; whatever good content we produced at wikipedia they can use. Everybody wins it seems.
Planetmath has however vastly superior math typesetting support since they integrate LaTeX. I am pretty sure that eventually a feature like that will be available on Wikipedia as well: you type $$ \sum_{i=1}^n i^2 $$ into a wiki article and TeX will convert the formula behind the scenes into a graphic to be included in the page. That would also be useful for chemical structure formulas and drawings. Such a system, called mathwiki, is running at http://www.mathcircle.org/cgi-bin/mathwiki.pl. The code is based on Cunningham's wiki.
Axel