I imagine the load wouldn't be a big deal.
An OpenID server is pretty
Yeah. I couldn't imagine it adding much load.
I've done several OpenID client implementations; so watching the
conversation with the server, it seems like there's no overhead at all
beyond a normal login sequence. So in a sense, that's where the overhead
is: additional requests to the login pages and scripts corresponding with
new traffic to the new openid client apps.