135mm Rear Spacing, But Using 130mm Wheel. Problems?

I've recently discovered that my 2011 Giant Roam-2 hybrid has a 135mm rear dropout spacing. I've been using a set of road wheels with 130mm spacing for about 1,000 miles. :eek:

How big of a problem is this? Can I continue or should I get a rear wheel with the appropriate spacing?

There are...