How many routes do ISP's and backbones announce to other backbones?

I have an idea that might solve the routing, prefix size, and router entry
size problem for good, and would allow even /31's to be published with
today's routers. But it's based on an assumption that I need to get
answered:

How many CIDR route entries do the backbones announce to other backbones?

I.e, how many routes does sprint maintain in its routers for uunet/alternet?
How many does mci maintain for (oh, foo, I know that there's 7 big ones).

How many routes does sprint maintain in its routers for the ISP's that
connect to sprint? For the ISP's that are connected to another backbone
(or would that be included in the previous paragraph, which I suspect to be
the case)?

Finally, how does a multi-homed site, meaning two connections to two
different ISPs, using two different backbone providers, actually work
in practice in today's internet?

		Michael