Little different from DEFCON or Threatcon levels in the military
Supposedly, there are some rough guidelines for what actions are appropriate for each level. As things were, we were already "on alert", so issuing further alerts were both confusing and counter-productive. For a government effort, 6 months to do anything is pretty fast. For example, how many years have they been arguing over things like the Food Pyramid? Some groups claim it reflects meat and dairy industry lobbying more than sound nutrition. As shown by this article, it only took the INS 6 months after the terrorist attacks to get around to issuing the hijackers their student visas that they had requested in 2000.