Use the class EntityFunctions
for trimming the time portion.
using System.Data.Objects;
var bla = (from log in context.Contacts
where EntityFunctions.TruncateTime(log.ModifiedDate) == EntityFunctions.TruncateTime(today.Date)
select log).FirstOrDefault();
UPDATE
As of EF 6.0 and later EntityFunctions is replaced by DbFunctions.