We hear so many good things about certain types of products and services that it's easy to take for granted that they will work for us. But when they don't, problems arise.

I've been noticing for years that GPS (global positioning systems) have wrongly placed my home a block away from its real location. That's annoying, but not a major issue; and I'm still a supporter of GPS and mapping Web sites.

Recently, though, I hit a snag that would have caused me great anguish if I had been dumb enough to believe the data.

I was driving with an associate to Rochester, N.Y., which is located near Lake Ontario in the northern part of New York. Google Maps on my desktop computer suggested we head due north from Pittsburgh; then ride east from Erie into northwest New York. Leaving at 5 a.m., we expected to traverse the 284-mile trip in 41/2 hours.

After reaching Erie, we decided to pull out the BlackBerry Bold Smartphone to see how many hours were left on our trip. This new phone includes AT&T Navigator, which seemed to be the perfect tool for our task. AT&T Navigator uses GPS to determine your current position; then, when you enter a destination, it computes the supposedly quickest route between where you are and where you want to go.

In moments, AT&T Navigator came alive -- and promptly directed us to take the next exit which was only yards ahead -- taking us off the main highway and onto a secondary road. It didn't seem right, so we passed the exit, hoping we weren't making a mistake and giving ourselves time to recheck our route.

I confirmed that I had entered Rochester correctly, but even trying repeatedly, it showed an erroneous route, in this case, taking us hundreds of miles off course.

After being on the road for two hours, AT&T Navigator wanted us to travel another 356 miles over the next 5 hours and 21 minutes. We would have ended up south of the Catskills.

I hadn't been to Rochester in years, so that was enough to make me check our original route with an alternate GPS.

So I pulled up Google Maps -- both on the BlackBerry Bold and on my laptop -- and found that our original route was correct. AT&T Navigator was hundreds of miles incorrect.

For the remainder of the trip, we relied on the Google Maps downloadable application, which continued to trace us along our route to the true Rochester (only 118 actual miles away, according to Google), and we arrived at our destination in time for our meeting.

After the trip, Mary Beth Lowell, communications manager at Telenav (the company behind the software in AT&T Navigator) and Telenav engineers looked into my Rochester navigation problem. They reported to me that I had tried six times to find Rochester without the ZIP code or street address.

Then the shocker: They had found two Rochesters in New York.

I have not been able to verify that the alternate Rochester exists. But even now, standing near my home, when I type Rochester, N.Y., into AT&T Navigator, it leads me to that unknown city near the Catskills, while typing the ZIP code directs me correctly to the home of Kodak and Xerox.

The Telenav engineers thought it was an isolated incident, but they committed to update their software to ensure that the duplicate Rochester problem is rectified.

In the meantime, anytime I use any GPS from now on, if it doesn't look right, I'll take a second look -- using a different GPS.