I do, too! We did run into a bit of a mess the other day, however, when a domain name somewhat important to us, that was thought to be on auto-renew, was expired. (I know, I know, big screwup) Our registrar then changed the name servers to their own. So we renewed it within a couple of hours, and we generally use our own caching servers, but some of our stuff out there is using google's DNS, and it seems they ignore the TTL for NS records, using their own TTL of, I think, 22600 seconds which equals more than 15.5 days. Ouch! The registrar sets a TTL on those of minutes.
I imagine it was a decision made to save resources. So, I think if google's DNS servers are being used widely, lesson learned from us if you ever need to change your domain's name servers.