Wheel balancing questions...

I have a question about tire balancing:
If you balance your wheels with traditional weights, what wheel positions do you get balanced, how often do you get them re-balanced and what does it cost to get it done?
If you use onboard balancers what positions do you have them on, what balancers do you use, do they work well and do you notice any fuel savings or better tire wear?
Thanks in advance!