Yes, I agree. This is something that I've been looking for lately.
It would also be great if GT5 itself had a leader boards.
I think I remember GT5P having a leader board for every track/car combination and replays of the fastest drivers.
It's helpful to have an idea of what a fast lap time on a certain track with a certain car is. I find that I can improve my lap time much more if I'm trying to achieve a certain time done by someone else rather than just trying to best my own time.