I have been using Outlook 2007 for quite some time now and have been using the RTM version for the last month or so. Anyway I have been noticing a slowing down recently in loading up Outlook and the new circle Hour Glass seemed to be sat "doing nothing". Well apparently a few other people have been experiencing this as well. This came up in one of our discussion aliases and Ewan Dalton has posted an excellent blogpost on this. This could be due to the added functionality of Outlook 2007 in having the ability to caching calendars. In a large organisation this can be an "issue" if you are opening up quite a few other peoples calenders at once. This is what was slowing me down in my case. I found I had 6 other peoples calendars open which were then synchronising everytime I loaded Outlook and started working in cached mode. And believe me our Calendars are busy !. To alleviate this problem untick the "Download shared folders (excludes mail folders)" configure this option as shown in the following screenshot.
Have a good weekend !.