I've been using Lookout for my last two 'droids. I've found that if the GPS is off, it won't locate the phone. I've tried several other locator apps with similar luck. So either I'm doing something wrong or the finder apps are easily defeated by disabling GPS.
I'm trying it now, GPS is off, and it won't locate the device. After several minutes of searching, it finally says it found my device... at a location dated June 18 of this year and several hundred miles from my current location.