Spoiled by Gmail
I use Gmail for my personal email and Outlook 2003 at work.
Once I’d been using Gmail for a while, I started displaying my work mail in Outlook by conversation, which is somewhat similar to Gmail. One difference, however, is that in Outlook sent emails are not added to the conversation, only received ones. So, at work I still find myself frequently digging through my ‘Sent Items’ folder to find emails that I contributed to an email thread.
In Gmail, I use tags for organizing my email. At work, I organize my email by putting it into folders. But in Outlook, if a new reply comes in for a conversation that I’ve moved to a folder, the reply goes to my Inbox and is not displayed with its entire conversation until I move it to the same folder. Frustrating.