Nolock hint

I have a SQL server database using SQL Server 2008.

I had an update performance issue and found that it block by a stored procedure select SQL.

I put with (NOLOCK) on the stored procedure and the issue is resolved.

My question is should I have NOLOCK every where on the entire application and what will be impact, will my database have better performance if I have NOLOCK every where in the database stored procedures?

I learn use SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED  can have entire database NOLOCK for all select clause.

I did it on my database, but I do not see any improvement for the database application.

Your information and help is great appreciated,

Regards,

Souris,