Haste is looking more and more awesome! However, we've taken the route of clojurescript/om for building on top of a Haskell web app. cljs just seems a bit more "there" as a compiles to js language. I would have loved to have used something like Haste or Fay, but for right now (taking a deep breath and giving up the type safety) I think the clojurescript eco-system looks the stronger for functional programming in the browser. The browser repl from emacs/lighttable is also a pretty impossible feature to beat!