There was some resistance in D3DX libs in the early days because there was a few bugs in it. If my memory is not failing me, the LookAtLH function would corrupt the matrix and not work correctly, but with DX8+ all the bugs are fixed.

ya like a previous poster said.. there''s more to them than just multiplying matrices and stuff. a lot of the functions are highly optimized and take full advantage of hardware that one computer may have but another may not.

you should definitely know how to write your own code for the math operations D3DX encapsulates but D3DX is so optimized that it''s almost dumb to write all your own code. D3DX is very excellently written and easy to use.