multiple wp’s from one install

Recently i’ve been looking to integrate my site(s) more tightly with wordpress and all has been going well.
However… At present I have two instances of wordpress running with a third likely as a global version. Updating any changes I make to each sites source files is becoming a drag, so I’ve been looking for a way to use one set of files from which I can then run each blog off of somehow.
I could have somehow included files from one central location into the existing file locations but this would involve lots of editing of files to make sure everything was relative and so on.
What I hit upon was that if I configure each install’s subdomain to point to the same folder they would obviously use the same files. In order to get each one looking at their own db tables I extracted the subdomain and use this value to vary the prefix for the db tables, eg blog1.moisie.net would create wp_blog1_ and blog2.moisie.net would create wp_blog2_ in the config file.
Based on the quick mock up I did last night (subdomains hadn’t updated properly so testing was limited) this method seems to be working fine, my question is: Does anyone have any thoughts as to if I would be likely to run into any errors? A blog is primarily defined by it’s config file so once that is setup everything else is seperate surely? I can’t think of anything but it helps to have some other brains.
Thanks in advance.