Outlook 2011 (For Mac) sometimes gets slow when it is syncing with exchange in The Cloud - A way to combat this, if the user has a great deal of emails, is to download the headers only.
This means that in the Inbox list, you get the Subject and the Sender of the email straight away, but the content of the email isn't downloaded. Once you then click on the email to view it, the content is downloaded (pictures, zip files, any attachments) It is worth noting however, that downloading an emails content isn't instant - You're hindered by the speed of the internet line.
Here's how to do it.
Apple>preferences>users>select user>advanced>check "download headers only"