Are you using block CSS in Emails? Non-inline styling.
I consider it best practice to ensure emails display as you intend them to put CSS inline. The way Marketo formats text if you change the color or whatever.
Where as a web page would have a separate file just for the style information, but you could also write it into the top of the page. You certainly can do this now, and some email browsers will chose to ignore it and others will do exactly what you intended.
So who's doing this? Block CSS in the header of your email. Who's using media queries? Are any clients supporting @font-face yet? What are you finding? Do you get complaints from people if they get a strange error? Tell me your results.
Re: Are you using block CSS in Emails? Non-inline styling.
For a bit of background, I've been seeing a lot more emails designed block css. Especially from places like the twitter feed @NeauConcepts. So I got one from them that's a progressive email, where if you view it on your iPhone it hides some long texts & inserts instead an open/close button. It looks really nice, but it only works on intelligent browsers, just defaulting to regular on outlook, etc.