Apple's office-oriented apps have had their fair share of updates. Exchange support is now built directly into the OS, supporting Exchange 2007 (SP 1) or later. Put your name, email address and password into Mail and everything's configured for you. After that point, iCal can be used to schedule meetings, Mail can be used to acknowledge meeting requests, and Snow Leopard in general can be used to blow a big fat raspberry at the incoming but distant Office 2010 for Mac.
ICAL EVENTS: These can now be opened in separate windows, speeding up workflow
Other changes to Mail and iCal are subtle but welcome (bar the typically unceremonious and simultaneous death of all Mail add-ons, many of which are being updated): Mail's sidebar categories can be reordered, and iCal events can be opened in separate windows or torn off to form separate windows if you stick with their default appearance.
Preview is the sneakiest app in the line-up, though. From Apple's press releases, you'd think it's merely gained the ability to enable smart text selection in PDF columns. However, you can also grab content from cameras, scanners and the screen. Give the app some brushes and layers and it'll be heading for Photoshop-Elements-combined-with-Acrobat territory.