Just a few random thoughts. Sorry they aren't organized in any sane fashion..
Remember to design in condensation traps. You need a trap at the lowest point in the pipe. This suggests you will need to maintain the standard 1/4 inch per foot gradient in the air pipe you run to drain the water to one end where you can stub it out. This suggests you will have to have a pit for the stub and drain valve. Failure to provide a condensation trap will result in rusted pipe leading to failure.
Not wanting to deal with condensation related rust is one reason people want to use plastic pipes. There do appear to be plastic pipes certified for compressed air. Schedule 40 water pipe is NOT one of them.
I had an old 1 1/2 gallon compressor I got cheap when I was given the 6hp, 30gallon compressor I now use. My kids wanted a way to fill their bike tires. I started looking at how to run a pipe from the compressor to the front of the garage. After much thinking I dug the old 1 1/2 gallon job out of the pile and set it up in the front of the garage. It works great for them. Makes me wonder if you really need a big air compressor at both locations. Maybe you can get away with a smaller one at one location or the other.
If you do decide to run an air line from your garage to your utility shed, consider installing an air tank in the shed. This can reduce the size of the air line you need to run. You can get a 5 gallon air tank for 20 bucks at harbor freight (
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=41712 ) and other places. Bigger ones are not that much more. You might be able to scrounge a tank from a shot air compressor if you are good at scrounging.
There are frequently threads on wiring shops. There is one now not far from this one on the forums. Given that you know you will need 110 and 220, many of us would suggest you install a sub pannel in your utility shed. Runs over 150 feet say you go up one size in wire. Thus while a 60 amp sub would normally require #8 awg, you should use #6 to keep the voltage drop under 5% for full load operation.
Any 110v outlet in your shed needs to be GFI protected.
I have not seen any 220v GFI units here in the US.
If you do take the time to run a full sub to the shed, maybe it makes sense to put a smaller air compressor out there, or haul one with you when you go.
Another thought is .. if you do decide to run a big honkin pipe between the shed and your garage, and you do decide to run a decent amount of power to your shed ... My big air compressor is L O U D. If I had a shed 150 ft from MY garage with a big honkin air pipe and decent power. I would surely move my compressor to the shed..
As usual, ymmv.