So, that function registers the font in Window’s list of known fonts for the current boot and sends a message to all of the open applications telling them to update their font cache. The part that’s locking up is the sending of that message.
In 7.1 we’ve fixed that by having a timeout on the font update broadcast calls. It may make the sync take a lot longer, so keep your eyes out for that. I’m almost certain it will, so some real-world experience would be very helpful.
We’ve also moved the syncing out of AE in 7.1 and into its own event script (so more apps can benefit). If you’re having trouble finding it after the update, look under “Tools -> Event Plugins” to configure and enable it.