The Shuttle is being rushed to return to flight and I don't really believe that anything they've done will prevent another Columbia disaster from happening again.
The Shuttle tile system for protection against re-entry is an accident waiting to happen regardless of the safety procedures put in place. At any moment, for multiple reasons, the tiles could fall off from the hull of the shuttle. Space debry could strike the shuttle and dislodge a tile even in orbit. So even if inspections are performed on the hull of the space shuttle in orbit, many things could happen before re-entry that would dislodge a tile in a potentially disastrous area.
That being said, previous missions have been flown successfully and have shown that this issue, if anything, is a minor one. Some risk is inherent in space travel, and will always be. You can't have a 0% risk in anything in life, and sometimes you have to live with a little risk. It's either that or you live in a bubble drinking apple juice your whole life.
But either way what NASA has done is more a PR exercise more than anything else as far as I'm concerned. The problem hasn't been solved, and what's worse we really don't know for sure that these new procedures would have prevented the Columbia accident from happening in the first place.