Wish Item: All Blog Access per Users

I'm building a couple of multi-user blogs and I'd like to have it so that a person can login to any one of the blogs within the one domain and post on any of the blogs within the domain structure. Registering for each and every blog is cumbersome and I'd restrict their access to "contributor" level. Is this possible now and I just don't know it? I've looked on codex for help on this, but everyone seems to shy away from this capability.