Ok, we have had the Z4 for seven months. It has been driven in the USA and we brought it to Germany in November 2005. My wife drives it to and from Frankfurt every four days on A3, so for the two hour and 20 minute trip four times per week it is being driven at 120 mph on average. Too bad it is a US Specs. Bimmer...
Handles very well at speeds up to 130 mph. Standard audio system is the best (10 speakers!!!). Little noise inside at high speed and even with the top down.
Gas mileage is not so good, but not an issue. Had to have the right rear light assembly replaced. leaked water and fried the stereo amp and battery compartment. No cost to us.