Use the class DbFunctions
for trimming the time portion.
using System.Data.Entity;
var bla = (from log in context.Contacts
where DbFunctions.TruncateTime(log.ModifiedDate)
== DbFunctions.TruncateTime(today.Date)
select log).FirstOrDefault();
Source: http://social.msdn.microsoft.com/Forums/en-US/csharpgeneral/thread/84d4e18b-7545-419b-9826-53ff1a0e2a62/