In Outlook 2003, you can change properties on multiple items at once. Some examples of when this is useful is to flag or set categories on the items.
1. Select the multiple items in the view2. Click the flag column in the default view - or - right click and set a category - or - right click and set a different color follow-up flag
OK yeah, this is a pretty weak tip, but I think the ability to do it without right click for flagging is pretty neat. :-)
Now if you could only do the same with "Add to Junk Senders"....
I actually played around with exactly that a few months ago, trying to figure out how to do that programatically. I tried to make it work by adding a button that would take the selected items, iterate through them one by one and activate the 'add to junk senders' button, but I think the problem that I ran into was that the selection collection is read-only. Someone more creative than I could probably figure it out though.