If you have been using Outlook 2007 and have never had performance issues with, you are lucky. Period.
Outlook 2007 was and probably is the most chastised of the Office 2007 suite of products today. Outlook 2007 took a hit with performance.
Despite having released numerous hot fixes and service packs, Outlook 2007 has not won many laurels. Time will tell if Outlook 2010 will outperform Outlook 2007 in the performance department!!
In the meantime see how Outlook 2010 TP has now donned the ‘ribbon’ just as SharePoint Designer 2010 TP.
Office 2007 did not have ‘the’ ribbon as compared to Word, Excel, etc.
Outlook 2010 TP has ribbon just as SharePoint Designer 2010 TP