Rico Mariani, our performance expert amongst other things, has a blog post detailing worst case peformance shown by LINQ to SQL in last May's CTP. You can see for yourself that performance really sucked. :-) Fortunately, that was the prototype and lots of low-hanging-fruit have been plucked since then. He's got a series of posts planned so I won't spoil them by revealing the end result now, even though it was my hand optimizing the code.