Sentai Filmworks (which sorta used to be ADV) announced today that they have licensed Gintama for release in the US!  The first DVD set will ship April 27th.  From what I can tell on the listing at Right Stuf, it will NOT be dubbed.  It has been airing on Crunchyroll for a while and I recall talk sometime back about Viz having the anime (they put out the manga).  The running time makes me think that they'll be releasing it in "half seasons" of about 13 or 14 episodes apiece.

 Update 2/4/10: Rightstuf.com has a sales promotion from Section 23 which include Sentai Filmworks. You can pre-order Gin Tama with a discount by using the coupon code "arrest" during check out.