One of the things I never cared for with Outlook Express is that they
promote the use of it in the background, but there was never any really good
notication for new mail arrival unless Outlook Express was maximized and you
were staring straight at it. When minimize it sat in your taskbar taking up
space and you missed notifications. I always thought the application should
have a system tray icon, so that you could get notifications and so that you
had more room on your taskbar.
Now Windows Live Mail Desktop says it offers notifications (still waiting to
see how that works), but I see no option to have it running the System Tray
(like messenger does). This would be the MOST awesome feature for this new
email client (my opinion - got lots of 'em too

)