Purchased mine certified used with 11000 miles on it. Very fun to drive! Looks fast, is fast. I rarely used to put the windows down in my old cars, but with this car I put the windows and top down every chance I get! I get many compliments on it--it is simply a sharp looking car and turns plenty of heads. I love how Z4s are not as widely popular as, say, a 3-series and that was a big reason why I purchased mine. If you're looking to buy, seriously consider the metallic silver color with premium package. With the sharp angles of the body styling, silver looks beautiful!
Great sound system, high mileage (25 in city!), low and smooth engine tone, smooth shifting, consistent acceleration from 0-90mph, responsive handling, killer body styling, and it is fun to drive!!
Low-end power increase, make the electronic steering less sensitive (very noticeable at low speeds), blind spots, object alert (long and low front end--can hit curbs easily if you're not used to it), cup holders stink, little storage space.