GroupWise has a nice feature (yes, only one). The message composition window in both fat client and web client has a "change item type to..." menu item. If you're creating an email message, appointment, or todo item, you can convert it to any of the other item types. The subject, body, and recipients of the message are preserved. Kinda like dragging an email message to the ZWC mini-calendar, but for new messages, and you can do the reverse, from calendar item to email. It's pretty handy.
I'm circulating this for input from other users before filing an RFE.