For the love of god, keep up with your maintenance.
I purchased my vehicle new as well (Feb. 2008). I went through the JB3 and currently have the COBB. I'm pretty satisfied with the power it delivers in Stage 2+ (FBO=FMIC, DP, Intake, Exhaust). I've done a few drag runs (best of 12.4 @ 111mph), and of course, the occassional spirited driving through corners/highways.
I didn't really baby this car, but I haven't abused it either. High mileage yes (around 62,000 miles right now), but it was mostly through high ways. So long as one stays away high torque usage, like standing starts/brake boosting, I think the TC will last a very long time. One would have to constantly abuse the drivetrain with the vehicles high torque to do some serious damage.
With that being said, I've luckily had no issues with the the diffs/transfer case. The most I ever encountered was the typical N54 fuel systems (plugs, injectors, HPFP).
However, just to be on the safe side, I've already done the preventative maintenance needed for this car at 60,000 miles. That includes Auto Transmission Fluid Change, Front/Rear Diff Fluid Change, Transfer Case fluid change, as well as oil changes at every 7,000 miles or so. Better to be safe than sorry.