How to measure the efficiency, load & performance of a script?

Hi all,

I was just wondering if any general tools / modules exist to help
measure the efficiency of any code.
I know that the Learning Perl books cover the theory but was wanting
to know if there were good measuring methods available.
Its pretty easy to figure out the time a script took to run but
knowing the load on the cpu, the overhead from all the loops &
variables, arrays & hashes, etc would also be nice to know.
Any suggestions appreciated.
Thanks in advance.
t.