I hate when that happens!!!!
This past weekend I was inspecting my coach's front tires. I was using a little picture chart showing various types of tire wear (and their cause), just kinda making sure mine weren't wearing uneven or getting cupped. I fired up the coach and turned the steering wheel hard right, then climbed out and looked at the right front. Lo and behold, a phillips screw right in the middle of the groove near the center of the tire!
To make a long story short, I checked the air pressure daily (no loss), then decided to make the 150 mile drive back home. When I got it home, I ended up removing the wheel myself and taking it to a Michelin truck tire dealer. They pulled out the screw (it was 1" long with half of it imbedded into the tread) and said it was short enough that there was no hole going through the casing to let out air. While I was there, I had them add the balancing powder beads inside the tire (and the filtered schrader valve guts to prevent the powder from making the valve leak). The screw removal was free (no flat repair), but the balancing powder was $15.
I do not regularly inspect my tires for screws or nails. This was just a chance fluke incident; -but I'm sure glad I saw it so I could take care of it and not have it bite me later down the road.