Two things I'd like to see would be the ability, through the GUI, to disable unneeded functionality. I don't use Apache, MySQL and other bits (though I appreciate they might be needed for the GUI itself), but it would be good - and better for security - if I could disable any parts I don't need.
Secondarily, some way to manage shared diaries and addressbooks, especially through Microsoft Outlook, would be a massively helpful feature... I know of no way to do this...?