Working with large models were very slow before the SP1, (have not tried it after the SP1, but it is said that is a snap now).
I still Design my tables first, then an in-house built tool generates the POCOs for me, so it takes the burden of doing repetitive tasks for each poco object.
when you are using source control systems, you can easily follow the history of your POCOs, it is not that easy with designer generated code.
I have a base for my POCO, which makes a lot of things quite easy.
I have views for all of my tables, each base view brings basic info for my foreign keys and my view POCOs derive from my POCO classes, which is quite usefull again.
And finally I dont like designers.
