Down in the (DU)mps:
http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=102x1611313
It is now 5:50 EDT and no retirement.
Drudge changed his headine briefly to say there would be an announcement tonight, but is now backing off and it just says "Report: Rehnquist to retire."
Looks like SCOTUS blog may be correct.
However, then again, Red State says this as an update:
"Update [2005-7-8 17:20:42 by Erick]: William Rehnquist, Chief Justice of the United States, has retired. A White House statement is forthcoming. Should caveat this: A very good source says this."