topological closeness....


On a global level, how useful would it be to base the decision
on whether the client address belongs to the the InterNIC block,
APNIC or the european registry ?

Little to none.

I can live with exceptions
such as an MCI customer in India gets redirected to the
north american mirror server instead of the one in Singapore
because their address belongs to an InterNIC allocated MCI

North America is topologically closer to India than Singapore (you go
through North America to get to Singapore from India).

How often do these exceptions happen?

Most of the time. The delegation of regional blocks is (arguably) an
administrative convenience. It has nothing to do with the network

Where can I
find the association of address blocks and registries?

Somebody else answered this.

We are currently working on mirroring a copule of sites on all
major continents.

In the Asia Pacific Rim region, nearly all the bandwidth goes from AP
region countries to the US directly. This is true due to the
tariffing situation, although it is now beginning to change (some
intra-Asia networks have already been established).

Putting mirrors in countries usually makes sense (particularly when a
country has an Internet exchange or two), but putting them on a
continental basis generally doesn't.