2008 335I with JP+ - All I can say is WOW!
First, let me say this - Terry at Burgertuning.com, outstanding job on the JB+.
I purchased my 2008 335i sedan used with 59k miles on it in Feb 2011. So far, so good. Other than a failed Oil Filter Housing Gasket that cost $750 in labor for a $13 gasket, no major issues.
I, as you, wanted just a little more kick. After a year of reading and researching, I chose the JB+ from Burgertuning.com. Installation took all of about 15 minutes. I drove the car for two days with "kid gloves". I wanted the computer in the car to have time to adapt to the new tune. Let me tell you - the patience paid off. By the 3rd day this car was a different animal. I usually drive my car in the sports mode (I have the auto with the paddle shifters) because the responsiveness is so much better then when in standard drive mode. Of course you sacrifice some fuel economy. Who said fun was cheap? Anyway, with the JB+ (oh, and a K&N drop in filter), the car now drives in standard auto drive mode, the way it drove prior in sport mode. The car is so much fun to drive that I forget I am in a sedan. Really! The best part, is when I switch the shifter to the left into the auto sports mode. Just today, I was sitting at a red light next to some punk kid in his 10 year old Honda Civic in bondo gray, huge ass muffler hanging out the back, chassis two inches off the ground and he gives me this nod with his head like, "Yo, you wanna go?" Before I had time to nod back, the light turned green and I pushed the gas pedal about 1/2 way down. Before the kid even had a chance to get off the line, I was at 60 in 2nd gear and passing thru the next light about 2 blocks away. I was tickled pink! I was giggling like a little school girl. OH MY GOD - what a rush! The power came on fluid and strong, the torque pushed me back into the seat like a rocket ship. ... and all of this with the JB+ set to the midway 50% mode as it came shipped. With the K&N filter and Shell 93 octane gas, this car is once again fun as hell.
So, to answer your question - for a daily driver, kid hauler, the JB+ won't disappoint based on my experience. Follow the instructions, let the car adapt to the add on tune for two or three days, put decent grade gas in your car, drop in a K&N filter and let the fun begin.