I'm curious. I have a number of blogs within my MovableType installation, Most are my own, however I also host a blog for a friend of mine. I can see at some point in the future that I will want to delete her blog.. however I wonder whether this will effectively screw up my database archives, because the numerical ID of each entry is based in the order of submission including all the blogs in the installation.

Will removing a blog affect the ID's of past blogs? Will the archival references remain intact? Or will I effectively be screwed?

Once 'issued' blog and entry ID's are not reused or changed, unless you export & reimport the entries or such. (even then they're not reused, just changed)

Thankyou very much Crys. I have been wondering whether I wanted to let other people use the same installation I do, for fear of messing up the database for later use.

I'm assuming then that when one deletes a blog movable type also deletes the entries in the database for that blog leaving the numerical ID's of the other blogs alone?

Right, when you delete a blog MT deletes the associated entries, categories, comments, etc. without touching the other blogs.