This would be huge. Outlook 2010 has an Insert > Screenshot feature that easily beats Gmail in convenience.
http://wisdom-soft.com/products/screenhunter_free.htm
We just recently upgraded to Office '07, so I'm guessing I'll have to wait another 3 years or so for the Office 2010...
Also, if you have OneNote running, at any time you can hit Windows+S to clip an area of your screen and copy to your clipboard. I use it all the time.