A request to developers of popular Linux distro Ubuntu seems to have revealed that Steam for Linux will launch some time this week.
spotted the correspondence, in which Canonical employee BryceH asked for some technical information about the distro citing, "These [details] are needed for the Valve Steam release that happens in a few days."
reported last week
that Valve plans a "private external beta for 1,000 users sometime in October," which is likely what BryceH is referring to. It will be possible to get into this beta via a sign-up page which has not gone live as of the writing of this article, but keep an eye on the
Valve Linux Blog
(and here, of course) to make sure you get your name on the list when it's available.