I have de-catted My 95 Disco TDI No Problems at all, If yours is a V8 Petrol or LPG, then you will have problems at MOT time, as it won't pass the emmisions without a Cat.
I have also de-catted my 56 plate Ford S-Max 140 TDCI and it now does 5 MPG more than before!
Having a 98 S plate Discovery and wanting to upgrade the exhaust system stainless is the way to go, But and a BIG BUT is can the cat be removed and left out of the system ?