It is currently the policy of the Clojure core development team to only accept requests to join the Clojure Dev Google group after they have received a signed CA (Contributor's Agreement) for Clojure. If you were interested in doing that, but have not already, details are available here: http://clojure.org/contributing
Note that there is no need to submit any contributions to Clojure before submitting a signed CA. Many people who have signed a CA have not yet contributed any patches to Clojure even after signing a CA.
If you have already submitted a CA, but it hasn't been processed yet, please wait until your name appears on the list of contributors on that page, and then re-apply to join the Clojure Dev Google group. Your request will be approved then.
The Clojure Google group (without "Dev" in the name) is open to anyone to join and discuss Clojure programming, including how it is implemented and any desired changes to the language. Most or all of the Clojure contributors belong to it as well.It is also possible for anyone to browse messages sent to the Clojure Dev Google group
Although it isn't the same as getting the Clojure Dev group messages in your inbox, you can browse messages on the web at http://groups.google.com/group/clojure-dev although I realize that isn't the same as getting new messages in your inbox. or get an Atom or RSS feed of them at http://groups.google.com/group/clojure-dev/feeds.