Whether EF4 is really ready for production is a bit hard to say since it's not officially been released yet.... but all the preliminary experiences and reports about it seem to indicate it's quite good.
However: you need to take into consideration what EF is trying to solve; it's a two-layer approach, one layer maps to your physical storage schema in your database (and supports multiple backends), and the second layer is your conceptual model you program against. And of course, there's the need for a mapping between those two layers.
So EF4 is great if you have a large number of tables, if you have multiple backends to support, if you need to be able to map a physical schema to a different conceptual schema, and so forth. It's great for complex enterprise level applications.
BUT that comes at a cost - those extra layers do have an impact on performance, complexity, maintainability. If you need those features, you'll be happy to pay that price, no question. But do you need that??
Sure, you could go back to straight ADO.NET - but do you really want to fiddle around with DataTables, DataRows, and untyped Row["RowName"]
constructs again?? REALLY???
So my recommendation would be this:
- if you need only SQL Server as your backend
- if you have a fairly simple and straightforward mapping of one database table to one entity object in your model
then: use Linq-to-SQL ! Why not?? It's still totally supported by Microsoft in .NET 4 - heck, they even did bugfixes and added a few bits and pieces - it's fast, it's efficient, it's lean and mean - so why not??