I played the original Grand Prix Legends demo almost every day for about 6 months. I seem to remember it was one car (the Lotus 49) and one track (Watkins Glen). Me and my cousin spent ages getting our laptimes down (I remember vividly the first time I got into the 1:12s there), talking about racing lines round the track, speculating about the full game... When the game finally did come out, in October of 1998, it was actually like Christmas, and I played literally nothing else for about 3 years.
And my eventual personal best lap at the Glen was a 1:05.4, which wasn't too shabby - and a full 7 seconds a lap faster than I was when I was still learning the demo!