There were few customer reports (http://forums.adobe.com/message/4392653) of icons going missing in files panel after the release of OSX Lion version 10.7.3. It was something which we investigated and worked with Apple to identify the issue and resolve it.
The update of 10.7.4 went live a few weeks ago and it was expected to fix the issue. The engineers have verified it internally and confirmed the fix. In the community also, there are no longer reports of the issue being raised anymore.
It is a good indication that Mac platform users, update to the latest available from Apple. So if you are running into such an issue, you should go ahead and launch Software Update installing the latest ones available in the list.