A user who would prefer to see the page's text as quickly as possible rather than to see the text in the font the page author prefers might have trouble expressing that preference with pages that use Typekit's solution. In other words, if the user would prefer to see the text rendered with a font available on the local machine rather than wait for a font to download for Typekit's servers, . . .
More generally, the mentality expressed in the original post (that authors need more control over what the end-user will see) has been bad for end users who want control over what they see without delving into extremely complex details, e.g., the profusion of complexity that is Firefox's about:config.
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A user who would prefer to see the page's text as quickly as possible rather than to see the text in the font the page author prefers might have trouble expressing that preference with pages that use Typekit's solution. In other words, if the user would prefer to see the text rendered with a font available on the local machine rather than wait for a font to download for Typekit's servers, . . .
More generally, the mentality expressed in the original post (that authors need more control over what the end-user will see) has been bad for end users who want control over what they see without delving into extremely complex details, e.g., the profusion of complexity that is Firefox's about:config.