Was just looking at my profile, and I notice that it incorrectly displayed my birthday as September 8th, rather than the 9th:
Looked in my settings assuming I derped, however they are indeed set to 9/9/86:
I tried changing it to 9/11 just to see what happened, and sure enough when I viewed my profile, it said 9/10. So, it looks like what's being shown in profiles is a day before what's actually configured. Purely cosmetic, not like I'm fretting over people thinking it's really on the 8th and getting all my birthday presents a day early (I accept Packers tickets, 1TB 2.5" 7200 RPM hard drives with RAID support, and cash). But interesting nonetheless.