Buy leathers now. Don't wait until you can "go fast". If you feel like you're going "fast", you're doing something wrong, probably not looking and planning far enough ahead. The track should feel like one fluid motion. Consistency is key to improving.
Here's some visual examples for ya...
Travis is pretty quick, done quite a few track days, but no formal training. On his day 1 video, you can see him fighting his bike.
http://video.google.com/videoplay?do...36778719357167
I was working on my own riding in the morning, so didn't get to work with him in the afternoon. We went over his video and talked about a few key points. Consistency, using his legs more, taking all of his weight off the handlebars, and lines. Now, watch his day 2 video and you can see a huge improvement in those areas.
http://video.google.com/videoplay?do...47514912413576
Jason is a track day junkie with no intention of racing. He's a big guy, like 6'6", 300lbs. He's done quite a few schools, and it shows in how smooth he is and how comfortable he is trailbraking. In his video, he actually catches me off guard at the beginning and I have to re-adjust, mentally, to follow him.
http://video.google.com/videoplay?do...99216404250748
Stephen is a guy I race against. He's really been working on his form and his corner exits in the off-season. We can't go above about 90% pace with the camera on my bike, because I can't tuck and it gets in the way. In his video, you can see a big difference in pace and riding style when compared with the other two.
http://video.google.com/videoplay?do...78478717817889