The newer model MacBook and MacBook Pro notebooks do take a while longer to charge up compared to their predecessors, this could have to do with the new power settings and the lower battery capacity found in these new computers; perhaps related to trickle charging, or it could be a firmware or software issue... hard to tell at this point, I'm not too worried about it though.
If you are really worried about this, do not hesitate to contact AppleCare about your concerns, I would imagine they would be more than happy to escalate up to a product specialist to investigate it for you further or provide you with more information.
