Significant (though not extensive) tile damage has been found on Atlantis, caused by an event just after 100 seconds into launch. The current view seems to be that it's significant enough to warrant further investigation, but the damage appears to be shallow and is in an area that is well protected. It is thus unlikely to have any detrimental effect on the mission (or on landing).
Press conference in 15 minutes (on NASA TV) should offer more details.
Source: Live commentary on NASA TV.
Not sure if it was artefacts in the footage etc. but I swear I saw 2 black specks fly off during the launch footage, maybe a minute or two into the launch, anyone else recall seeing anything?