Despite the great interface changes to Outlook 2007 - its slowness and [Not responding]messages are major obsticles to the application that is always open and in use.
There have been a number of articles (such as Outlook 2007 is slow) pointing to size of mailbox or indexing services as being problematical but there is nothing definative. Operating in cached mode with large inboxes seems to cause instability. (This is hightlighted by the MS article Planning for Cached Exchange Mode deployment in Outlook 2007 - this is a very complete article however seemingly self contradictory. Whilst it states that "the Unicode OST files can store up to 20 gigabytes (GB) of data", and it recommends thier use, further down the document it says "One factor that can contribute to reduced performance is a large OST file. If the user's OST file grows too large (for example, larger than 1 GB), Outlook with Cached Exchange Mode performance degrades."
So yes you can have a huge OST file but it will be completly unusable in cached mode....!
Additionally opening a new message in the reading pane can be painfull, even without embedded graphics which slow it down even more. Im running on an XP Centrino Duo with 2Gb of RAM so it should cope well but it just doesnt.
If anyone has performance pointers to make this otherwise impressive program perform Im sure Id not be the only one to be greatful?