Referencing a single table from all tables in the database At current, I have around 130 tables in my database, anticipating a growth of circa 200 tables in total.

Now I have several tables (well, most of them, actually) that contain properties like CreatedBy / ModifiedBy / DeletedBy, which take an nvarchar(MAX) as their data type and contain the name of the user.

This makes versioning a lot harder, because the name of the user might change during the lifetime of the application.

Now I've thought about referencing each and every *By-Column via a Foreign Key to the users table. However this would result in 600 foreign keys on a single table (expecting the 200 tables with 3 foreign keys per table, if not more).

Are there any drawbacks? What's the best practice?

As a side note (not relevant for the dba aspect of my question, I presume): I'm using Entity Framework in C#, only referencing a single part of it in my code (because I don't want and don't need 600 collections in my User class).
You may want to consider a Type 2 slowly changing dimension table and normalize your user name data. This will give you a better picture of whom is changing the data over time and allow you to use a smaller more efficient surrogate key for your *By columns.