I am wondering why 302 redirect is being used instead of 301.
The previous poster's quote: "which has the same effect on visitors' browsers and SE crawling bots" is not entirely correct.
302 means a temporary redirect. It means the search engines will keep trying the old url (in this case, the wordpress.com url).
301 means "permanently moved", so Google e.a. will transfer the authority they attributed the old wordpress.com with, to your own domain.
(source: Google's Matt Cutts http://www.mattcutts.com/blog/seo-advice-discussing-302-redirects/ )
If you have bought a custom domain mapping, that means that you actually want to move your blog, and the "google authority" it had, to your own place.
The way it's done now, gives a bit of a "sneaky" impression: that WordPress would like to keep (and redirect to its own pages) the traffic once you have decided to actually move out and transfer the wordpress.com mapped domain to your own hosting...