I've read through the volumes of docs regarding WSE 3.0 and it seems that
using X.509 certificates for message-layer security is a highly effective way
to handle the variety of security concerns we have when implementing B2B web
services.

Being a relative X.509 newbie, I have a question of a logistical nature.
Let's say I'm hosting multiple web services accessed by multiple business
partners. Certs in this context are generally pegged to URI's, aren't they?
In that case, can't I use a single cert if all of my services use the same
root URI with virtual directories? Then, of course, each client must have
it's own cert with whom we exchange public keys. So we'd be providing the
same public key to all of our business partners. Am I missing something here,
or is this scenario feasible?

Cost is probably the biggest issue when considering an X.509-based solution.
If a single cert will suffice, cost is really no longer a factor from our
perspective.

Please let me know your thoughts. Thanks.