It is still under construction and is scheduled to be completed in June 2010 per http://www.hooverdambypass.org.

BTW, there is a really cool webcam on their website that is remote user controlled. It is at http://live8.truelook.com/hooverdam/bypass.

Cheers,
Bill

PS Some of those Google Earth images are several years old so in a lot of cases it is not a very good tool to judge how far along a project is.