From what I've read, using regular in a car that calls for premium won't harm the engine the way it did years ago--the onboard computer will automatically adjust ignition timing to compensate for lower octane rating and prevent knocking. But the car's performance won't be what it would be on premium. There's no benefit to putting premium in a car that calls for regular.
I've never noticed any difference using Premium in any car I've ever owned. My 2001 PT Cruiser that I briefly owned actually stated in the owners manual not to use Premium. It said performance could be degraded because the engine was tuned to run on 87 octane. It said use 89 or above only when doing heavy towing, etc.
