If you want to learn a language from the perspective of getting something done (in the startup webapp sphere), go for Python/Django or Ruby/Rails - they both have mature, well-established communities with plenty of documentation and available libraries.
Clojure seems quite cool, but it's a relatively new language and, especially when compared to the other two platforms mentioned above, it lacks the wealth of institutional knowledge about delivering good webapps that forms a significant portion of the value of Rails or Django.
Clojure is the exciting new thing you blog about. Rails or Django is what you used to write the blog itself.
Seeing as someone has already built a fast and scalable blog using Clojure I'm not sure your arguments holds any water. Having used both Python/Django, Python/CherryPy/Mako/CouchDB, and Clojure/Compojure/CouchDB I'd say that Clojure is a pretty damn capable web application programming language. And compared to my experiences with PHP+SQL, it is light years beyond.
Clojure also has an extremely rich _core_ library of functionality - a lot of things that would simply be more work in Python or even Ruby can be expressed more succinctly in Clojure (yes I know Haskellers won't be impressed ;)
As far as communities I've found #clojure IRC orders of magnitudes more helpful than #django or #python (and both those channels aren't bad).
There's something to be said for starting with a language that has great library support. While one approach to learning is to write from scratch, another is to read existing code and be able to build what you want to build using parts that are already there (less likelihood of losing your enthusiasm out of frustration too). Clojure does have Java library support, but it's native library support doesn't match that of Python or Ruby or Java.
Clojure seems quite cool, but it's a relatively new language and, especially when compared to the other two platforms mentioned above, it lacks the wealth of institutional knowledge about delivering good webapps that forms a significant portion of the value of Rails or Django.
Clojure is the exciting new thing you blog about. Rails or Django is what you used to write the blog itself.