Update 2017-01-22: Added V.QQ.com clip and links.
Update 2011-05-12: I'm sorry, I just realized/remembered that of course Youtube is blocked in China. I will research some way to upload this video to a video site accessible in China.
I'm teaching a course on writing e-mails for business, with the first class focusing on tone: formal, neutral or casual.
I've also just started watching a British comedy series called The IT Crowd, which has a funny scene directly related to this issue.
Here's the clip (or click here to see it bigger on Youtube):
For people in China, I have found the clip on V.QQ.com and have embedded it below. The part about e-mail starts at 1'54".
In fact, V.QQ.com offers viewers in China the chance to watch the whole series:
G.A.L.E.S.L. / joe3
Some tips and links on learning English.