Linq到SQL DataContext的多个/单个实例

I have a project with a number of different classes querying and modifying data in a common set of tables. I've set up a .dbml file which provides us with a DataContext class. My question is whether a single instance of the DataContext should be used by all objects, or whether multiple instances are safe to use. I'm also wondering about thread safety in the case of a single DataContext, and whether access to it's methods should be synchronized.I have a project with a number of different cla