LINQ-to-SQL vs stored procedures?

I am generally a proponent of putting everything in stored procedures, for all of the reasons DBAs have been harping on for years. In the case of Linq, it is true that there will be no performance difference with simple CRUD queries.

But keep a few things in mind when making this decision: using any ORM couples you tightly to your data model. A DBA has no freedom to make changes to the data model without forcing you to change your compiled code. With stored procedures, you can hide these sorts of changes to an extent, since the parameter list and results set(s) returned from a procedure represent its contract, and the innards can be changed around, just so long as that contract is still met.

And also, if Linq is used for more complex queries, tuning the database becomes a much more difficult task. When a stored procedure is running slow, the DBA can totally focus on the code in isolation, and has lots of options, just so that contract is still satisfied when he/she is done.

I have seen many, many cases where serious problems in an application were addressed by changes to the schema and code in stored procedures without any change to deployed, compiled code.

Perhaps a hybird approach would be nice with Linq? Linq can, of course, be used to call stored procedures.

Some advantages of LINQ over sprocs:

1. Type safety: I think we all understand this.
2. Abstraction: This is especially true with LINQ-to-Entities. This abstraction also allows the framework to add additional improvements that you can easily take advantage of. PLINQ is an example of adding multi-threading support to LINQ. Code changes are minimal to add this support. It would be MUCH harder to do this data access code that simply calls sprocs.
3. Debugging support: I can use any .NET debugger to debug the queries. With sprocs, you cannot easily debug the SQL and that experience is largely tied to your database vendor (MS SQL Server provides a query analyzer, but often that isn't enough).
4. Vendor agnostic: LINQ works with lots of databases and the number of supported databases will only increase. Sprocs are not always portable between databases, either because of varying syntax or feature support (if the database supports sprocs at all).
5. Deployment: Others have mentioned this already, but it's easier to deploy a single assembly than to deploy a set of sprocs. This also ties in with #4.
6. Easier: You don't have to learn T-SQL to do data access, nor do you have to learn the data access API (e.g. ADO.NET) necessary for calling the sprocs. This is related to #3 and #4.

Some disadvantages of LINQ vs sprocs:

1. Network traffic: sprocs need only serialize sproc-name and argument data over the wire while LINQ sends the entire query. This can get really bad if the queries are very complex. However, LINQ's abstraction allows Microsoft to improve this over time.
2. Less flexible: Sprocs can take full advantage of a database's featureset. LINQ tends to be more generic in it's support. This is common in any kind of language abstraction (e.g. C# vs assembler).
3. Recompiling: If you need to make changes to the way you do data access, you need to recompile, version, and redeploy your assembly. Sprocs can sometimes allow a DBA to tune the data access routine without a need to redeploy anything.

Security and manageability are something that people argue about too.

1. Security: For example, you can protect your sensitive data by restricting access to the tables directly, and put ACLs on the sprocs. With LINQ, however, you can still restrict direct access to tables and instead put ACLs on updatable table views to achieve a similar end (assuming your database supports updatable views).
2. Manageability: Using views also gives you the advantage of shielding your application non-breaking from schema changes (like table normalization). You can update the view without requiring your data access code to change.

I used to be a big sproc guy, but I'm starting to lean towards LINQ as a better alternative in general. If there are some areas where sprocs are clearly better, then I'll probably still write a sproc but access it using LINQ. :)