Re: Xprofile: Just show first Letter of last name
Here is what I would do… And what I do mostly on all of my BuddyPress installations…
In your BuddyPress->General Settings, make the “Full Name field name” be called “Display Name” or in your case “First Name/Last Initial”
That way, people know right away what you want shown there. You won’t need to baby sit them because it says right there what you want entered. Most people will follow suit, and the ones that don’t, what’s the diff?
(Notice I use my middle name here on bp.org?) 
Then, create extra fields for First Name and Last Name, for yourself to use. Make them visible if you’d like, or whatever.
This way you’re not trying to create a crazy filter to micro manage anything.
