Here and there on the web, people mention the following best practice for Windows Phone SQLCE databases:
Use binary _version column to improve performance.
Ok, what’s that? Well, when you want to define such a row in SQL, you would then create a rowversion column (not a binary(50) column…).
When such a column is created, it is updated when the row is updated. Linq apparently uses this to prevent some concurrency conflicts. (I still need to dig a little on that subject… 
)
So this column:
[Column(IsVersion = true, IsDbGenerated = true, DbType = "rowversion not null"]
private Binary _version;
would be created in SQL:
Alter table mytable
add _version rowversion not null
Happy coding