Most people keep the same PSI, though dropping 1-2 will improve ride and handling at the cost of increased wear. Nitrogen is nice if you go to the track or live in an area with wide temperature variations and don't want to check your pressure occasionally. Otherwise, not worth the cost.
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