Once you have it set up you will be able to see and manage your calendar and address book. You will be able to search the ExchangeLabs directory. All of this is done over SSL so your communication is safe even at Starbucks. And if you loose your iPhone, you can go to the ExchangeLabs web site and remotely wipe your phone.
The only weakness is that the iPhone only supports one Exchange account at a time so if you already have an Exchange account, you cannot have two. You would have to configure one as IMAP/POP3 without support for calendaring and email.