Personal PDAs – do you let users sync them to your Exchange server or not?

At my organization we have officially supported PDAs which the company pays for and we say that we don’t support users’ personal PDAs but have not been so strict in doing so. I looked at Tech Republic’s Cell Phone & PDA Policy for guidance and it leaves the door open, only saying users can’t sync unauthorized PDAs without prior written consent from IT.

But what I need to know is: do you let your users sync personal PDAs with your servers at all? If so, is it to cut costs (after all, they’re paying for the service already)? If not, what are your reasons? Security, I’m assuming, but I’m going to have to make a strong case to my CFO since we have budget constraints and it seems like a tempting option.

Thanks.