Microsoft made available the Troubleshooting Performance Problems in SQL Server 2008 white paper on their site. This white paper is 102 pages long, the scope of this white paper is limited to the problems commonly seen by Microsoft Customer Service and Support (CSS).

Below is what is covered in this white paper:

Introduction
Goals
Methodology

Resource Bottlenecks
Tools for Resolving Resource Bottlenecks

CPU Bottlenecks
Memory Bottlenecks
I/O Bottlenecks
tempdb
Slow-Running Queries
Extended Events 80
Data Collector and the MDW
Appendix A: DBCC MEMORYSTATUS Description
Appendix B: MDW Data Collection

You can download the Troubleshooting Performance Problems in SQL Server 2008 white paper here: http://msdn.microsoft.com/en-us/library/dd672789.aspx

If you are currently thinking about upgrading to SQL Server 2008 or if you are already using SQL Server 2008 then you should definitely check out this white paper.