I have had the 2006 GS 300 for about 2 months now. I was bouncing all over on what to get and what sold me on it was the luxury and fuel milage. I drive about 35 miles to work each day and average over 30mpg on the highway cruising at about 75mph. (One tankful, I got 33mpg on a trip.) I'm getting about 24mpg in the city. All this with absolute quality and luxury that you get with Lexus. The performance is solid - it's no rocket, but I didn't buy it for that. One of my friends just got a new BMW 525i at the same time and dollar for dollar he will even tell you I got the better value.
To many to mention, but just the solid feel and of course the gas mileage. It's really just as good as a hybird.
Just a slight bit much of throttle hesitation when you hit it hard from a stop.