OK I'm gonna say this and I may say it badly so please forgive me.
Bettermost is a closed community, Oh anyone can join but because so many of the active participants have a shared history it is harder for a new comer to make a mark, to break in, unless they have an poignant or unusual story to share or they are just brassy and jump in with both feet like I did. It's kind of reminds me of high school that way. Completed with the cliques, the behind the scenes drama and the gossip. You have the admins who are those really smart, cool and well known kids who ran for class president. You have the old time posters who everyone knows and fall into their various categories from geeks, socs, know-it-all's, class clowns, cheerleaders, etc... including those who feel very left out of all the fun and have no idea how to join in and that is why their post counts are low and eventually they drift away.
Most people who fill out that little form when they join do not realize that their birthday is going to end up on the calendar. I certainly did not and I wasn't asked if I wanted it there. There are cultures and religions that do not celebrate the day of one's birth. Do you want to run the risk of offending someone who has different cultural or social beliefs than your own?
Who decides? Right now I see "Happy Birthday" messages everywhere for the regulars, usually started by their friends or admirers....but if it becomes a "banner" event then you must recognized everyone or no one and either way you run the risk of offering offense or of hurting feelings. I just see it as a slippery slope fraught with more peril than pleasure and think it would be a mistake.
The limited space on the banner is better utilized as it is being used now, for forum news, current events, and focusing attention on outstanding threads and poster achievements (with member permission)