I personally ride a new Bianchi Pista, and although it is one of the more economy-level "track" bikes, I think it was well worth the money to have a nice new shiny bike. I was considering trying to do a conversion, but I figured shelling out a little more (ok, a few hundred more), to have all new parts and everything was worth it.
I'm curious how others feel: If you are riding an older road frame, do you find yourself wishing you had a "true" track bike? If you are riding a track bike, do you wish you had just bought a fixed rear wheel and thrown it on that ten speed in the garage instead?
And I know everyone isn't either riding and old road bike or a new track bike; If you are riding an older track bike are you happy with it? (A friend of mine who currently has a new aluminum track bike sometimes says he wants to go back to an old lugged steel frame..)