Shared content in Exchange is very common request, and not just for contacts-- calendars too.
WICKSoft (www.wicksoft.com) provides a solution for Exchange 2003 that will let you view/edit public and delegate content from your BlackBerry.
It's not synch or a 'copy to your personal folders' solution-- as gibson_hg pointed out, this could be a problem if you have a lot of contacts or a very busy shared calendar. Instead, it's a direct interface to Exchange, not BES. The advantage to this is that anything you change on the phone gets updated on Exchange immediately.
You can get an trial copy over at our website.
Will