Voltage on the grounded conductive devices when plugging in non-grounded outlet
Plug config. doesn't really matter in case of AC supply as long as you don't have dual supply systems (in some countries you can get both DC and AC supply on request to your house) .

Having an Earth connection is a good safety measure since the electrical wiring wears over time due to the heat produced in conductor inside and the aging insulation around the wires ,which will start to conduct electricity slowly over time .There is chance that at some point of time the insulation of whole electrical circuitry in your house could fail and can cause electric shock of max. supply voltage while using home appliances due to leaking current .

And also Earthing provides safety for the circuit itself avoiding/delaying possible fire accident due to shorting between the Live and Neutral wores incase of failure of wiring insulation .

Summing it all up ,I'd suggest you to change all your sockets in the house to 3 pin sockets (with dedicated Earth supply I mean) and provide proper earthing and use appliances with earth connection as much as possible .