oakmontoz! Thank you. I revised it slightly to work a bit easier without changing messages color. This offers the same functionality with less impact on sent messages if people already had them color coded . See below :
1 - Create a rule in the Mail Preferences pane
2 - Call it "Get My Paperclip Icons Back!"
3 - Set conditions as below :
A - If ALL of the following conditions are met :
B - From Ends With [Your email address here] (you can do this for multiple too]
C - Any Attachment Name Contain "." [with the quotations around the dot]
Perform the following actions :
D - Mark as Read [which really makes no impact on how its viewed]
Click Ok. When message "Do you want to apply your rules to messages in selected mailboxes?" I chose "Dont Apply". [But you can click "Apply" if you are in the "Sent Folder"
Then go to your sent folder, Select your messages [recent/all], and right click "Apply Rules" or from the menu Message -> Apply Rules.
Voilla! Paperclip icons are back. Plus "Mark as Read" did no harm to your already colored/flagged sent emails.
Hope this helps!
Note : If you could make this rule apply automatically when you send mail, well... until Apple fixes this problem, this would be the seamless solution. Until then, you would have to do it manually.
Oh, and if you want to automate iBiM's above workaround so that all new sent messages retain their paperclips, Indev's $24.95 Mail Act On software allows you to automatically apply rules to outgoing mail.
I've been using Mail Act On under Snow Leopard for years and it's a wonderful piece of software. However, I haven't yet installed it under Lion (I only moved to Lion yesterday, forced there by the imminent closure of MobileMe). So, as always, I'd recommend downloading the Mail Act On trial version and testing it before spending the $24.95.