What have you found Python to be best for when doing web apps and what development sets do you most commonly use?
It will never be as fast in execution as, say, C (though we can expect impressive speed improvements through the improved use of VMs); but in terms of developer productivity you can't beat a high-level dynamic language.
For any complex app, you need good project management software, version control, unit testing, clear and comprehensive documentation, and so on. I can't think of any reason why you can't apply these techniques using a dynamic language.
~90% of the web apps you're using on the web are written in scripting languages.