Erik,
I have used Typekit in the past and am currently working to implement Google web fonts.
This solutoin is not ideal but one thing that I often do is code most of my landing pages in Adobe Dreamweaver so that I can see a decent preview. Then I will drop in my code inside html blocks on the landing tool within Marketo.
For the Typekit or Google fonts javascript calls I typically set that up at the template level.
One thing to be aware of is some web based fonts can impact landing page load time. If your web font style is pretty simple you should be okay though.
Hope that helps.
Patrick
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