I'm an intermediate driver running an 11 M3 that's stock except for upgraded brake fluid and pads, but honestly I don't feel that I should be timing myself at this point. I think the knowledge that I was timing myself would subconsciously change the decisions I make, and not for the better -- plus I think I still have enough general technique to learn/improve (throttle steer, trail braking) that using times and telemetry to compare lines and such isn't necessary yet.
Also my insurance coverage isn't in effect when I'm timing myself, and I suspect the reason for that is the psychological impact that timing has. I read an article on the Nurburgring where the officials said that when there's an accident, 80% of the time the driver was using some sort of timing device.
Likely selling end of 2015:
11 M3 E92 Le Mans | Black Nov w/ Alum | 6MT | Premium 2 | Convenience | 19" | EDC | Prem Audio | Moonroof | BMW Apps | Yoko AD08 R | Vorshlag Adjustable Camber Plates | StopTech ST-60 380mm BBK | Castrol SRF Fluid | ModMyNav.com rear camera | ECS Tuning Sunglasses Holder