"do you have one configuration table for all the environments or has each environment its own config table?"

We maintain one configuration table per ETL server (because each physical machine can have only one environment variable - that has the config information in it)

If it is the latter one, why use a .dtsconfig file?

That portion is mostly useful for developers to easily repoint their configurations to a different table or server for testing if need be.

Another question: why don't you store the packages in the MSDB folder? Do you have specific reasons to do that? My preference is the file system - and it just lays out nicely for the process we use.

This article probably moved me to this method - http://bi-polar23.blogspot.com/2008/06/ssis-and-sql-server-agent-choosing.html

And to end my reply: I think a nice addition to the article is an explanation on how to configure your packages using the configuration table. E.g. using the package configuration wizard in BIDS (of which you have 1 screenshot).

(Noted - my thinking was this was covered pretty well elsewhere, but maybe not)