I agree Bottle is simple and has some nice features, but I'm a little wary of the decorator-based "micro"frameworks. In my experience it can lead to strange code structure and it's more difficult to translate into the class-based handlers of larger frameworks.

Moreover, I don't think the barrier of entry to use Tornado, for example, is significantly higher than Bottle, and you can use it for any sized project. I realize that is both a server and framework, but truthfully I guess I'm also wary of WSGI on the whole and wouldn't recommend anyone even start down that rabbit hole in this day and age.