We may be nit picking here, but I think there may be conditioning differences between kegged and bottled beers. I too notice that the first beer I open, while it may be fully carbonated, is usually not as good as the next one a few days or a week later. Like ruascott, I too am usually anxious to try one, and usually open the first one after only 6-9 days in the bottle. Since I prime my IPAs to around 2.5 volumes, they're usually carbed after that time, but they do continue to improve in flavor over the next week or two.
Understand that kegged beers are force carbonated, while bottled beers undergo a second "mini" fermentation in the bottle. I'm not surprised that they continue to improve some, even after they are fully carbonated.