Edit:
Press Release from VeriSign: [verisign.com...]
This is great news for those of us who work with database driven sites, no more risk of loss of data between propagations when changing to new servers!
Except that this has nothing to do with the time-to-live (TTL) for your domain - it only affects new registrations in this way. Propagation of the new nameserver info for an existing domain will happen as before, dependent on your TTL. (A DNS guru will surely explain this better than me!)
This is great news for those of us who work with database driven sites, no more risk of loss of data between propagations when changing to new servers!
It only affects changes to the TLD zones. It has no effect on changes in your domain's zone, ie changing the IP address of your webserver.
They have lowered the TTL value to 15 minutes, but that only affects negative caching (how long you assume a "domain doesn't exist" response is valid for). They haven't changed any of the other settings in the SOA record. ISP DNS servers will still cache other records for the same amount of time.