RE: VeriSign's rapid DNS updates in .com/.net

Petri Helenius wrote:

What would be your suggestion to achieve the desired
effect that many seek by lower TTL's, which is changing
A records to point to available, lower load servers at
different times?

On a similar note (and not viewing the issue through
the usual spam-colored glasses):

Some people are using low dns TTLs in disaster recovery
setups, so that in the event of a disaster at a primary
site, services can be switched over to new servers at a
secondary site via easy and fast DNS changes? If the TTLs
are too long, all the cached records will continue to
point at the servers which might no longer exist -- until
they expire. This is another situation where low TTLs
can be beneficial.

Are there any other uses for low dns TTLs that haven't
been brought up in this thread?

And what is a "low TTL" being classified as? 30 minutes?
10 minutes? 5 minutes?