I consider this a bug and a dangerous one. I was excited to check out the e-Newsletter plugin until I discovered that it created 7 tables for every single site (currently around 300) in our network when I only activated it on 1 site!
I did NOT Network Activate it. I simply installed it and then went to a single site and activated it locally to that site only. This is not good at all. Now I'm faced with cleaning up a bunch of tables manually. I don't want all that extra junk in there - I try to keep things as tightly optimized as I can.
I only discovered it right away because I was going to do a manual import into the raw tables of existing email lists since there is not (yet) an import function.
Can you provide a way to clean up those tables from all the sites the plugin is not active on? And fix it so that a local activation does not trigger table creation for every site in the network?