..the prevailing one, however, seems to be: "if you are able, write your own; if you are not, use Webware or Twisted."
Part of a more rigorous answer would involve knowing what sort of app you're writing. If it's fairly static and simple, you could get away with Cheetah and some glue. Mid-range...try Webware, or Zope if it's self-contained. Modpython is like modperl--just language hooks into the webserver, so it's not really an "app framework"--you need to build something on top of that. Twisted is more of a glorified socket handler than an app framework.
My current project needed a flexible DB layer, so they were all out. I wrote my own on top of mod_python and/or ASP.