A couple of things that I notice right away is that the IP addresses are easy to remember:
188.8.131.52 and 184.108.40.206
That's actually something I am going to be able to recall next time I find myself with broken DNS services. The second thing is that my ping to these are 24ms roughly, that's not too bad. The real test is lookup speed, and this is where Google is riding on the edge as they appear to be doing some aggressive pre-lookup of DNS entries on slow DNS servers. Are they going to break TTL? A lot of people design fail-over using a lower TTL in their DNS responses so that the cache will be flushed if a failover is needed to a new IP address.
In any case, I've giving it a go for a while and so far my surfing does feel faster.
So if your public facing users are complaining about a slow web experience on your site, one suggestion is to point them to the free Google DNS servers to see if that improves their experience.