What would happen if the customer used private address space and NAT
& ALGs to hook this into the two providers' CIDR space? At worst,
address space consumption would be doubled (if the customer really
needs a full /24 internally), but when we're talking about a couple
of /24s versus routing yet another prefix, I think that's preferable.
Has anybody noticed that the net global routing table has bumped 40k
a couple of times recently? Would the registries have problems with
this approach?
Another issue is that the I-must-be-multihomed-to-different-providers
mantra frequently isn't anything else than a funny idea in somebody's
head.
Per Gregers Bilse <bilse@EU.net> writes:
What would happen if the customer used private address space and NAT
& ALGs to hook this into the two providers' CIDR space?
I think that this is an excellent idea.
In fact, Ed Kern at Digex is working with OFRV on making
this real, so that other folks can do so when the NAT code
is available in IOS. He might have something to say about
your note.
Has anybody noticed that the net global routing table has bumped 40k
a couple of times recently?
Yes. Fun fun fun. Has anyone else seen SSE microcode
size get too big as a result? Ping. More than 2/3 of the
way to the point where 7000s+SSPs will not be usable with
traffic towards a fair number of destinations, in routers
that carry full routing.
Would the registries have problems with this approach?
Would it matter if they did? 
No, seriously, any concerns about the cases where twice
the PA address space will be used should be releived by
the reduction in demand (or at least in absolute need)
for PI address space. In short, if it works well enough
to be a general solution for customer migratability
without requiring migratable address allocations, it's
obviously a net win for the registries too.
Another issue is that the I-must-be-multihomed-to-different-providers
mantra frequently isn't anything else than a funny idea in somebody's
head.
Well, I agree with you about market misperception.
However, this doesn't seem to be a very popular thing to
say (flame wars ahead), and in part this is because few
people have been saying it in public, even when
they actually agree.
Sean.