One of my goals this week while I am in the US is to get closer to the answer to the above - by attending LINQ sessions, talking to product folks, talking to my colleagues and.... having a good old browse around the internet. The following post from Adam caught my eye. Definitely worth a read along with the links within.
At this point I believe LINQ has lots of potential to become the primary way for developers in ISVs to access relational, xml and other data but not the only way - in other words the question above is very valid to ask as LINQ is not right for everything.
I will post again in a week or so after I have absorbed all the information...
P.S. Good luck Adam with your new software venture