I have not used EF yet, but have done a little with Linq to SQL which is somewhat similar, although not as robust. One of the issues with Linq to SQL is that it passes string parameters using their length so that Select * from person where first_name = 'Bob' and Select * From person where first_name = 'Steve' generate 2 query plans because it parameterizes the call and sends a varchar(3) parameter the first time and varchar(5) the second time and it may also be nvarchar so if your column is varchar you have an implicit conversion taking place as well.