Capabilities of Exchange Forms Designer are poorer than that of Outlook. You should consider using Outlook instead. About Outlook Forms Perhaps the most dramatic advantage of Outlook in regards to forms is its capability to create, install and run forms. Outlook provides powerful functionality, which allows for creation of usable MAPI forms in a matter of days instead of months. This comes with its price, though.
Performance is one aspect here.
Also, Outlook forms are only a subset of all possible forms. For example, you would not be able to create something like the Checkers form. Visual interface elements are limited to edit boxes, buttons, and some other common elements. Code should be written in VBScript. Everything is event driven.