There is a piece about this in this month's Roundel. Basically said that the ECU varies the coolant temperature under various conditions so much that it can give "useless" information to the driver. BMW is eliminating coolant temp gauges in all their cars for this reason.
2011 BMW 335d, Space Grey/Black, Sport, Premium, Cold Weather, Convenience, Nav, Harman Kardon/Sat, iPod
2010 Audi A4 2.0 Quattro P+ 6MT (Wife's car)
2004 BMW R1150RA