As scottsvb mentioned above, Gustav has probably been with us for awhile now, it's just that ambiguous satellite data and a lack of surface or recon data until this afternoon led to an overly conservative estimate regarding its intensity. It doesn't quite have the look of a storm that is rapidly intensifying, but steady intensification at the very least seems to be underway and likely to continue in the near term. Like Fay, Gustav's fate will be determined by how it interacts with the numerous land masses along its potential track, but it appears that Gustav will be stronger than Fay ever was before encountering any of those land masses.