+2  A: 

There's a pretty good post that I read a while back that outlines some testing and analysis of GPT in a variety of scenarios

+1  A: 

I use GPT at work since 2007, and I totally satisfied. I use it to monitor and optimize a Linux network library, and I have obtained a significant results.

The main flaw of GPT is the lack of precision. Due to the design, you only got the main time consuming functions, but this is often what you need when you want to optimize a program.

To be more precise I advise to use other tools like gprof or IBM Quantify.

Steve Gury