Irene is a huge system, and will take time to consolidate, and thus strengthen. The CDO appears to be completely missing Hispanola, which is not good for us in the US since it means the interaction with the mountains will be minimal. It also means it is further north, and thus right of track. Based on IR history, I would say this is more likely a wobble due to the land interaction with Puerto Rico than an actual track shift, but that is not guarenteed.

Using the outermost feederbands, the storm is 700 miles across, though the center is very much toward the southwest of that total cloud mass. As the system deepens and spins up, the storm will shed the outer cloud bands and consolidate toward the core, an area I estimate to be around 100-125 miles in radius (200-250 miles in diameter), which makes it around the size of some of the larger diameter storms that occur in the Atlantic. This will slow it's strengthening (the shear size of it makes it more difficult for it to organize), but the SSTs are hot and very conducive to strengthening, so it might take less time than most storms would.

Keep an eye on the storm if you are anywhere from Florida through New England. Even if the storm misses landfall, we could have a major beach erosion issue for the entire Atlantic seaboard. Right now it looks like the gulf is out of the threat cone, but hurricanes can be erratic, and long range forecasts often change as the storm draws closer.

Edit: Spectacular animation showing Irene developing:
http://www.nasa.gov/mission_pages/hurricanes/archives/2011/h2011_irene.html