I have an entire box of Pokes with it. It spreads to other pokemon when you battle, so if you ever get it, fill your team with pointless Pokes, fight a few battles, and when the other 5 are infected, throw 'em in the PC, then repeat. This ensures you have a 'test tube' of Pokerus at your disposal, and you can spread it to a Pokemon you want to EV train at your own leisure.
Looking back at my EV training, I really don't know how I could keep my sanity without it. That cuts it in half, and then Macho Brace cuts it in half again. That means to max out an EV of 252, fixed with both PR and MB, you must battle 63 Pokes instead of 126, with just MB, or 252 without either. Granted the pokes you're fighting give you 1 EV. But if you're smart enough to do the Secret Base trick, with each Poke giving you 3, that cuts the amount to 21! But since you can only fight SB trainers once a day, you have to do some work outside.