About StarForce reversing.
As far as I know there are two groups which managed to completely reverse StarForce VM. One Spanish and second Russian. Part of their work is available on the Internet (including VM description).
About drivers.
They are harder to protect but easier to reverse. For instance look at Hasp and Xtreme Protector drivers. They are hard to maintain (compatibility) but gives strong anti-debug shield in NT OSes clones (Pace/XProtector). Anyway, that's the endless story because cracker can always use ring0 too.... until the time someone will invent "ring -1" mode
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About debugger detection.
Sometimes it's not enogugh to skip it. If you want to keygen serious protection then, usually, you have to unpack it... althought it's not always necessary (for instance look at ExeShield tutorial).
Regards.