Caliper query

Ok, so over the weekend I changed my brake pads. First time I've done it on the SV because every other time I've had the bike in for work at the same time, so laziness meant I'd just ask the mech to do it while he was doing everything else.

Now I'm wondering if that was a bit of a mistake, and hopefully you guys can set my mind at rest. Thing is that the metal shim from the back of the piston-side pad is missing. Two questions:

1) The brakes haven't been bad at all, so is this part strictly necessary? I realise they're cheap so I'm going to order some anyway, but I'm just wondering if...

2) Their absence might have caused any problems at all.

It's part number 12 (59171-33D00) in this fiche: http://fiche.ronayers.com/Index.cfm/.../FRONT_CALIPER

Cheers!

Thats the anti squeal shim m8, had a few bikes with those missing, not really a big issue with braking performance. Just ensure you have a nice smear of copper slip on the BACK of the pads.