Mechanism of reduction by elemental sodium
When alcohol molecules adsorb on the surface of the sodium metal, an electron can be transferred from sodium to the alcohol O-H bond with simultaneous disproportionation  (homolytic cleavage) of the O-H bond thereby generating the alkoxide anion and a hydrogen radical.  The hydrogen radical (probably still on or near the metal surface) can then go on to dimerize and produce hydrogen gas.



EDIT: Support of Mechanism

The mechanism proposed above involves a single electron transfer (SET) from sodium.  This is based on the fact that:


All dissolving (sodium) metal reactions, such as the Birch reduction of alkynes and aromatics, proceed by the SET mechanism 
Other reactions involving sodium metal such as the acyloin condensation, the pinacol coupling, the Bouveault–Blanc reduction, etc., proceed through the SET mechanism
The reaction of sodium and water still proceeds in the gas phase where ionization seems less likely, but electron transfer still viable.


Searching on-line I found that water can solvate electrons just like ammonia can.  The chief difference being one of stability; in ammonia solvated electrons are stable for days, whereas in water they are stable for less than 1 msec.  Given the preceding mechanistic evidence and the fact that solvated electrons can exist in water, it seems reasonable to suggest that the mechanism of alkoxide formation, when sodium is reacted with an alcohol, also involves the SET mechanism.