I did it and I'm still alive. (Of course the ladder must be dry. )
Actually you don't have to be earthed or be touching another wire to be fried.
If depends on the frequency. At low frequencies your capacitance will be negligible so only a tiny current will flow, at high frequencies your capacitance will be significant so a high current can flow giving you a severe burn. Luckily higher frequencies don't shock you so much but the burns can be pretty nasty.
The ground resistance depends upon how moist it is. For even low values of moisture the resistance is likely low enough to cause a lethal current through your body from a power line.You say that if you stand barefoot on the ground and touch the live wire then current would flow through your body.
But the ground resistance is very large, so isnt it still considered an open circuit?