Today Microsoft released service pack 2 for Office
2007. You can get it from here service pack or use
Windows Update. From my point of view,
very important are modifications done with
Outlook.

Microsoft Office Outlook
  • Performance improvements that apply to the following general responsiveness
    areas:
    • Startup
      Removes lengthy operations from initial startup.
    • Shutdown
      Makes Outlook exit predictably despite pending activities.
    • Folder View and Switch
      Improves view rendering and folder
      switching.
  • Calendar improvements
    Improves underlying data structures and the general
    reliability of calendar updates.
  • Data file checks
    Greatly reduces the number of scenarios in which you
    receive the following error message when you start Outlook:
    The data file ‘file name’ was not closed properly. This file is
    being checked for problems.