How many seconds until the bomb detonates in the Counter Strike: Source

It hasn't been replaced. Counter-Strike: Source is still there, but Valve opened up the beta once more for everyone.

As for the changes, it seems nothing visible has been done yet, only bugfixes and performance testing.

They did this to test certain new features to the engine without breaking the main game, a valid concern for one of the most popular multiplayer games of all time.

Are you looking to do something like what RAZER did with portal two? Theoretically, it is possible as you would need the driver for your mouse to read like a joystick. The first mouse could be read as the left stick and the second mouse would be read like another joystick. As far as I know you cannot bind it that way, BUT, if you find a flight stick driver you could try to reinstall the mouse with that driver temporarily or find a program that could read mouse movements as a flight stick and then in CS:S you would map the buttons as walk look and switch weapons.

There is no good program to do want I have outlined. I would try to use a controller for what you want to do instead but that is me. I doubt that a program can differentiate between two optical mouses, and map their actions to joystick functions but it isn't necessarily impossible.