If you use a high voltage divider as Oren described it should work right nicely under evaluation conditions. Please be aware however that with this solution there are a number of factors to consider for production type products:

1) This scheme causes your microcontroller system ground to be referenced to one side of the power mains. Most safety agency regulations would not permit such product to have a user interface with metalic access or other ground connections to user accessable equipment.

2) AC Mains almost always exhibit high voltage spikes due to high current inductive load switching. Any divider solution needs to have appropriate clamping circuitry to prevent the spikes from coming through the circuit and putting an input to the A/D that could be 2x or 3x or more over the nominal input range. Note that spikes with fast rise times often can do more damage to semiconductors in a system due to their ability to couple through the capacitive paths in the circuit.

3) The components needed to interface with the AC mains need to have ratings sufficient to prevent component failure. Resistors with even 1 mA flowing through them at 220 VAC will be dissapating more power than a typical surface mount resistor is capable of handling :o). I know that here in the US, safety registered equipment typically requires that components that interface with the power mains need to be either UL rated or need to be investigated according to UL guidelines during product certification.

......A small UL listed isolation transformer is sometimes a good idea.
Michael Karas