Thanks. I've noticed this too in one install. I'll a note to the installation instructions for people updating.
I think I've working out why this is happening. Before 1.2, the font list was cached for 12 hours, and refreshed automatically. From 1.2 the fonts are cached indefinitely, and refreshed only by going into the settings page and saving. On upgrading, the cache will last for *up to* 12 hours, and then be flushed by WP, and then the Google Webfonts won't be accessible, at least until the admin saves the settings.
What I should have done, on an upgrade to 1.2, is resave the cached fonts in WP without an expiry time.
So apologies to anyone who have found the fonts suddenly disappear - just go into the settings page for this plugin and save, then they will be back.