That sorta makes it sound worse, honestly, if databases in MongoDB are anything like you'd use the word for in any other datastore. A global lock across all databases is mind-bogglingly confusing; what's one DB got to do with another?

Couldn't you just work around that before by running a separate Mongo process per database?

Saying it's now on the database still means any single-database app is globally locked. Or does using Mongo imply you're going to be making lots of databases so this actually means anything?