In the just released new episode of GT.TV, there is 21 minutes of news on all things Valve. What are they working on, what games are coming out, what other features are coming soon and what is GabeN doing on vacation. Also, the Linux beta is mentioned to be coming "fairly soon". Definitily worth a watch if you like to know more about Valve's current developments.
how he said very soon seems almost like in 1 or 2 months, and since there is that possible hint that its coming out by the end of this year, it would be a resonable date (since beta would probably go on for 2-3 months