Gayatri,
Perf in SSIS is a huge area. There's no doubt that the dataflow can be a screamingly fast data movement vehicle but you need to know how to use it properly.
Regarding memory utilization, maybe this will help: http://blogs.conchango.com/jamiethomson/archive/2005/05/29/SSIS_3A00_-Memory-Usage.aspx
-Jamie
