On the subject of birthdays, the recent proposed profile page redesign/Vox/LJ-is-for-teenagers kerfuffle has quite reasonably resulted in LJ wanting a better idea of what the actual age distribution of its users is.
The problem is, there's no way to tell them without either telling the universe exactly what one's birthday is, or telling no one at all. LJ has some very handy little ways of letting its users know what birthdays are forthcoming among those on a friendslist, but this only works when the date is shared. There's no way to share just the date and not the year, so many only list the date - leaving LJ with no idea how old their average user actually is. I have no real objections to people I know and trust knowing this sort of information about me. I do object to random online people knowing so easily - it's just one more piece of data which risks identity fraud, and there's no point compounding the problem when so much is already available so freely online. I'm feeling indecisive as to what to do about this right now - up the average LJ age, or keep what birthday information I have here publically available.