I used Dancing Script in an email, thinking that another script-like font or at least something attractive would be substituted in cases where the font was not available - but many people received an email with the text in Comic Sans, which is just awful. The email was a huge embarrassment. Is that a problem on CC's end or with individual email programs?
We do have a feature request in to make fonts more customizable, and to improve the formatting to increase the consistency across devices. Ultimately each device can read the coding differently, and some devices will simply have a different display than others, sometimes with unfortunate results. Putting extra coding in to ensure that consistency can sometimes lead to too much HTML in the background, which can cause even more extreme problems though. We'll continue working on ways to improve consistency and add more font options, but ultimately if you're using a non-standard font, there's no guarantee that it will display the way you want in all email clients.