I've been and am on both sides of the GPS is good/micromanagement discussion. The GPS companies do a great job touting their product, and GPS is a great tool if you suspect that someone is cheating. We've all seen techs that cheat companies, and most of them get caught, on the same hand companies have cheated us, and they eventually loose their techs and then their customers.

Crown in Atlanta had GPS years ago. Their techs left in droves and the ones left learned quickly how to disable the system. It may have saved the company a few bucks in the short term in hours and fuel, but the long-term cost was prohibitive in lost customers (they could not get their equipment fixed) and increased hiring and training costs.

The real problems facing any company today are scary. Company vehicles are becoming targets for people on the road who want a free insurance ride, techs are 'encouraged' to get to the customers more quickly, skip that lunch break and eat and drive etc. These types of things have driven the cost of insurance through the roof. Couple in the tripled price of gas, and any one offering to save you money on vehicle expenses is listened to. I've tested GPS on vehicles, in both cellular and satellite forms. It's amazing that the drivers know we are testing it on their vehicles and the gas usage goes down, and we get less calls complaining about 'that crazy driver'; the downside is big brother is watching. We tested on volunteer's vehicles, and that was still a comment.

I suspect that we will keep looking at GPS or something like it. When it's offered by the vehicle manufacturers as an option we will get it. The gas savings are too real; the insurance breaks are real, as are the OBDII fault codes coming into our fleet manager (from the GPS system via e-mail). These have saved us significant down time and vehicle expenses. How the GPS info on route and driver speed is used will be open for discussion. Excess speed is a valid safety issue, as is what happens to vehicles after hours. With the service vehicles we use we have ignored where they are between 5AM and 6PM, too many stops, and to be honest too time consuming to work out, before and after is a lot more interesting. Speeding is tougher to work out, though >75 mph is emailed to the manager and the tech. The downside of GPS in the cost of the unit; its install costs and on going monthly service fees.
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We are also in the process of having our vehicles speed controlled to 70 MPH by the manufacturer. Not as easy to defeat, only a one time cost, and this also gives us an insurance saving.

This really boils down to companies being abused by techs, and techs not trusting their management to fairly use a tool. If you're a good tech you'll leave (I've done it and seen it), a 8-5 mediocre tech will stay, and eventually the company itself will be mediocre..
We've noticed that by slowing the vehicles down we've achieved a lot of the same savings I fuel and insurance..

My apologies if I rambled..