You can probably save a few trips to the database by not using the AddOrUpdate extension method. Here is a simplified version of your code.
protected override void Seed(Jobboard.Sandbox.Model.JobboardContext context)
{
var defaultTemplateGuid = Guid.Parse("xxxxx");
var defaultTemplate = context.Templates.SingleOrDefault(
t => t.Guid == defaultTemplateGuid);
if (defaultTemplate == null)
{
context.Templates.Add(
new Template
{
Guid = defaultTemplateGuid,
Name = "Default Template",
Content = "Some Default Content"
});
}
}