I read somewhere else that Mac OS X Server 10.5 will implement Time Machine on a network level. If you run an all-Mac shop or workgroup, Retrospect might have just been obsolesced. The devil is in the implementation, though, as always.
It would be a very good idea for Apple to build in an easy to configure VOIP/PBX system based on Asterisk. Wirelessly integrating it with iPhone is a killer concept that Cingular no doubt won't like too much.
The whole point of iCal Server is to provide a good alternative to Exchange on the back-end that works well with a wide variety of front-end products. Building up that kind of ecosystem with other open source and commercial producers is the only way that Exchange's iron grip will be broken. If it interfaces seamlessly with Outlook, I could see a lot of SMBs migrating away from Exchange and Microsoft's usurious CAL fees.
http://www.roughlydrafted.com/RD/RDM.Tech.Q1.07/8DFEC70D-ED31-46AD-B23A-558AF0473F91.html
You can already set up an Exchange-like server for integrated email, contacts and calendars using Kerio Mail Server 6.1. It's an excellent product that works well with iCal and Address Book, but I think Apple can do even better with contacts and calendaring. Apple would have to improve their mail server a lot to catch up with Kerio and Communigate Pro, however.