I've used the conditional syntax in WHERE clauses, but a conditional ORDER BY? That essentially guarantees not using indexes, and ORDER BY without being able to use indexes tends to be VERY costly. A conditional where clause is a linear growth (N growth), whereas a conditional ORDER by would entail something like hash sorts/bubble sorts (N^2 growth), so the effort grows polynomially.
Are you actually ever seeing it use anything index related using that technique? I'd be really curious if you did - I just don't see how it would.
----------------------------------------------------------------------------------
Your lack of planning does not constitute an emergency on my part...unless you're my manager...or a director and above...or a really loud-spoken end-user..All right - what was my emergency again?