Question: I am developing a applicatin which are having more than 5000 users once upon time. I using
ASP.NET 3.5 framework for developement. I want to develope a high performance DAL Layer
using latest technolgies like linq,ADO.NET Entity,ADO.NET Data services. I also want to make sure that it shuld be generic to all the future developement. Can any one pleasae Let me know which pattern i should use to develope that Database Access Layer. I am also
want to use microsoft enterprise library for that.

Answer: 
I think you should look at NHibernate and Fluent NHibernate. 

You could save yourself a lot of time by not writing your own DAL. Only you know your non-functional requirements around perf and whether you're optimizing for reads, updates or something else, so write some tests, prototype, and see how it goes.

My personaly opinion is that Microsoft Ent Lib and perf aren't best buddies, but again you should prototype and prove this early in your dev cycle.
You can use [Linq to SQL](http://msdn.microsoft.com/en-us/library/bb425822.aspx).

You can also take a look at [this article series](http://krisvandermotten.wordpress.com/2006/11/19/creating-a-data-access-layer-with-linq-to-sql-part-1/) for creating an actual DAL using the same technology.