I use arc and Racket for rapid web development. I use them because I like coding in lisp. Having said that, it's only fast if you've got experience with it, otherwise it is a long slog.
Basically, the ecosystem just isn't as good. There is no Heroku for lisp. Want a library to help out with API access? You must write it yourself. Want to make a get request from arc? You must write it yourself. Etc.
Yes (for some value of significant). There are lots of lisps out there - I know that Scheme / Racket / Arc have some nice features that make them good for rapid prototyping, such as continuations, macros, and powerful REPL. Having said that the ecosystem is incredibly important, I think history has shown that a good ecosystem for a weak language is more successful that a strong language with a weak ecosystem.
It's hard to explain exactly, but having macros means that you don't need design patterns and frameworks as much (among other things). You just sort of code, and make macros as the need arises to solve whatever problem you encounter.
Having continuations means you can focus on the flow of the application, and don't have to set up controller / URLs for things, you just code the function directly, and it makes it really easy to implement whatever flow you want (e.g. ask for a login only after a user posts a comment).
The REPL means that you don't need to restart the server to see any changes, you add in whatever changes you have and you can see the results right away, which makes for a really interactive development environment.
When you add it all up, it makes for a pleasant environment to work in.
Basically, the ecosystem just isn't as good. There is no Heroku for lisp. Want a library to help out with API access? You must write it yourself. Want to make a get request from arc? You must write it yourself. Etc.