As you probably know, Outlook 2003 and older use Exchange Public Folders for their Free/Busy data and Offline Address Book. You may also know that Exchange 2007 and Exchange 2010 have deprecated Public Folders in favour of an HTTP-based distribution method for the data, which Outlook 2007 & 2010 fully support.
One could then reasonably conclude that removing public folders in an Exchange 2007 or Exchange 2010 environment might negatively affect Outlook 2003 and older clients. This is technically correct, though the reality is slightly more dramatic; it completely blocks Pre-Outlook 2007 clients from connecting to your Exchange servers and presents the users with a handy “Your administrator has blocked this version of Outlook from connecting” message.
What this all means is that if your support team have spent the last year lying to you every time you’ve asked them how they’re progressing on upgrading all the remaining Outlook 2003 installs to 2007/2010 then when you remove the last public folder store from your Exchange environment you’ll suddenly have hundreds of people whose can no longer access their emails. This, for some reason, upsets them.
The moral of this story is that you should never trust what people tell you, because they’re almost always lying bastards, and make sure you verify the information for yourself before making any changes. Yes, it’s a lot of work and no, you shouldn’t have to do it, but it’s always you that gets the flak when it all hits the fan.