System services....anything important in there I should leave on?

[ticklemypickle]

Currently have them all off, doesn't even really tell me what they do.

 

[Steve28]

Cell network search: helps to narrow down what cell networks to look for based on where your phone is
Compass calibration: north and "magnetic north" deviate a different amount depending on where you are.
Diagnostics & Usage: so. Apple knows where you when crash reports are sent in
Location based iAds: seems obvious
Setting time zone: seems obvious
Traffic: again, seems obvious. Although not sure how this data is used at apple

 

[andrewshah]

I believe traffic is used to update the live traffic view on Google Maps. I'm guessing it takes into account your current speed while driving and uses the data to update the maps.