I'm certain it's a one time cost. Though I suspect that given that Closure [optimizes out unused code](http://blog.fogus.me/2011/07/21/compiling-clojure-to-javascr...) the more I use of the goog namespace, the larger that baseline will become.
That being said, 30k is the size of minified jQuery, so folks that are alright with building apps on jQuery won't find 30k to be that terrible.
EDIT: sorry, I meant larger pure ClojureScript code base.
As a point of reference, their sample twitterbuzz app which uses the Google Closure library is 100k minified.
That being said, this is alpha software so it's hard to criticizes it's lack of output optimization at this point.
Kinda wished they had stopped at the language and left the DOM out of it.
Still, very cool.
[1] http://news.ycombinator.com/item?id=2783060
[2] http://www.hanselman.com/blog/JavaScriptisAssemblyLanguagefo...