<p>If I have hundreds/thousands of client computers WCP'ing to my server, should I respond with a '200 OK' type message stating that I received the data and stored it in the db successfully?</p>

<p>Is this already built-into WCF?</p>

There's 2 ways you could do this - return a value from your wcf call indicating success or failure, or assume success and use a callback to tell the client if there's a problem.
My preference would be to use a
one-way
service call with a
duplex service
and use a callback contract for the service to notify the client of a failure. There's a good description of callback contracts
here
and
here
.
I think you get a nicer, more asynchronous architecture if you follow the second path, but for simple applications just returning success or failure may be easier.