Me too. I'm addicted now - even bought a 2nd FG to ride at the velodrome as my 1st FG has road geometry and doesn't work at all at the velodrome (head tube is too tall, and bottom bracket is too low -> pedal strike).

Given the bottom bracket on a track bike is higher, and the head tube is lower, your saddle will be higher on a track bike, but your handlebars lower - leading to the positioning in carlton's pictures above.

Just speaking in frames in general (road or track), a larger frame is more comfortable, and a smaller frame is more sporty (I'm talking a 2cm difference here). Given a track bike is meant for racing (if you are riding on the velodrome), you may find yourself with a slightly smaller frame on a track bike. 1 to 2cm smaller is not unusual (4 cm is not going to work).

Your best bet - rent some bikes at the track of your choice, see what fits and feels best, and then you will have some good knowledge when you are ready to buy.