An attempt at a shootout: http://colorstudy.com/docs/shootout.html (implementing a Wiki).
Another currently ongoing attempt: http://pyre.third-bit.com/pyweb/index.html (implementing a Library Book system).
One way to compare WebProgramming frameworks would be to have the same application coded in all possible different frameworks.
One possible candidate would be a feature comparison: displaying and editing the data defined by WebProgrammingTemplate.
Other popular candidates: web poll (perhaps too simple), web log, ...