If you would have made a single sided ARM board it would have been a "first" and would have never worked to spec.
I designed a single-sided breakout board for the Luminary 3S10x series. But those have only 28 pins and run at 20MHz, and I never actually built it so I don't know whether it actually worked. The design phase itself was pretty "illuminating." "In what way is a 28pin ARM chip different from a 28pin AVR chip?" (7 power supply pins and 4 "extra" jtag pins start the list...)