Runying Mao and Len Wyatt did a great study of SSIS performance, and posted some results:

Getting Optimal Performance with Integration Services Lookups

http://blogs.msdn.com/sqlperf/archive/2007/04/24/getting-optimal-performance-with-integration-services-lookups.aspx

OLEDB Source with Views 

http://blogs.msdn.com/sqlperf/archive/2007/04/29/set-up-ole-db-source-to-read-from-view-efficiently.aspx

BLOB and buffer temporary storage

http://blogs.msdn.com/sqlperf/archive/2007/05/01/set-blobtempstoragepath-and-buffertempstoragepath-to-fast-drives.aspx 

SSIS Performance Counters

http://blogs.msdn.com/sqlperf/archive/2007/05/01/something-about-ssis-performance-counters.aspx

Buffer size adjustments

http://blogs.msdn.com/sqlperf/archive/2007/05/11/adjust-buffer-size-in-ssis-data-flow-task.aspx

Parallel execution

http://blogs.msdn.com/sqlperf/archive/2007/05/11/implement-parallel-execution-in-ssis.aspx