I'm not sure there is anything more pretentious than marking an email as High Importance. I am not any more inclined to read a red-flagged email than one that isn't MARKED WITH EXCLAMATION POINTS.
Actually, there is something email-related that is more pretentious: requests for receipts of email. Does anyone else get these? One of the dean's secretaries ALWAYS put one of these on emails she sends out. After I open the email, Outlook pops open a request for permission to send back a receipt of reading. Ummm.... no. I always click no. If people are concerned that I read an email, why not request IN THE EMAIL that I acknowledge reading it?
The funny thing is that usually these requests are attached to emails that clearly aren't urgent. Things like regalia order requests. Or lab report questions. Or fall book orders.
What do I consider topics worthy of the red flag? Notifications of free food. Or booze. Or cancellations of classes. Yup, that's all I can think of right now.
(By all means feel free to explain to me why URGENT! is an important feature for emails.)