The grignard reagent will convert ketones to tertiary alcohols through nucleophilic substitution and protonation of the carbonyl oxygen. As for grignard reagent's effects on alcohols, I am pretty sure that is a definite no-no in the real world, since grignard reagents will violently react with any acidic proton. Thus, you don't use grignard reagents in protic solvents, like H2O, since it would only attack the acidic protons...instead, grignards are used with aprotic solvents like diethyl ether. I hope that helped. 🙂
I remember reading that alcohols are not reacted with grignard's becuase it just breaks them into Mg2+ X- OH- and RH ...this is why a lot of strong acids are not used with grignard reagants(strong base).