UPDATE: Bethesda has slightly altered Dishonored's release date, moving the game back a couple weeks to October 9, 2012 (October 12 in Europe).
Bethesda and Arkane Studio's Dishonored will be releasing in the United States on September 25 this year if two accidental pre-order listing is to be believed. The information was leaked after both Best Buy Canada and FutureShop.ca accidentally listed the date.
Which, by itself, isn't all that interesting, but it gets much more fun when you consider that's very close to the the highly anticipated juggernaut from Gearbox, Borderlands 2, releasing September 18 and 21 (US and UK respectively.) It's starting to look like we'll have a bit of showdown that week. Though if we were Bethesda, we'd be trying as hard as possible to get the new IP out of Borderlands 2's shadow.
Still, Dishonored may be able to hold it's own. Arkane is a very solid studio with credits like Arx Fatalis, Bioshock 2 (assisting the main developer), and an unreleased Half-Life project on their resume. If you haven't yet, you should check out the Dishonored debut trailer that released a couple weeks ago.