DNS cache hold of SERVFAIL responses

[list at satchell.net (Stephen Satchell)]

This is for any Google admin on this list:

When you receive a SERVFAIL from a name server listed as authoritative
for a given domain, how long is that negative look-up cached?

When you receive a SERVFAIL from the root servers, how long is that
negative lookup cached?

Does Google follow RFC 2308?

Is there a common cache for all resolvers, or do each resolver in your
DNS server corps maintain a local cache?

When a SOA (when you see one) says 14400 for the minimum TTL (or
negative cache TTL) does Google honor that hold time?