I've been using Office 2010 beta for some time now and I switched back to the 2007 version for a couple days on a different machine and boy did I miss Conversation Threading. It think this will be the greatest addition to Outlook in the last 10 years. I know Gmail has had a similar feature for a while, but it's nice to see stuff like this in the corporate world.
Essentially, it works like this: You get cc:ed on a message with 4 other people. 3 people respond, then you respond, then somebody else responds. Now you've got 5 messages in your inbox, and one in your sent box. With Conversation view, your inbox only shows the most recent message, with a drop down arrow to show you all of the messages in the conversation,
including your sent message. You can also move that conversation to another folder and all future message for that conversation will appear in that folder. Lastly, through with a conversation (you know, the mass CC where everybody unsubscribes via reply all)? well you can mark the conversation for ignore and all future messages from that conversation will be automatically deleted without seeing your inbox.
I would show you a picture of this in practice, but I have too much private information in my inbox. You'll have to rely on this video:
http://www.youtube.com/watch?v=FV_QOeA3L7g
