This blog here describes some very usefull usages of strace:

Find out which config files a program reads on startup

strace php 2>&1 | grep php.ini

Why does this program not open my file?

strace -e open,access 2>&1 | grep your-filename

What is that process doing RIGHT NOW?

strace -p 15427

What is taking time?

strace -c -p 11084
You can also run this "start to finish", here with "ls":
race -c >/dev/null ls

Why the **** can’t I connect to that server?

strace -e poll,select,connect,recvfrom,sendto nc 80