How to know how many processes each user is running?, there are lots of ways to do this, I've found this some time ago in the ubuntu forums I think.
I can not find right now a real scenario when you may need this, but it is a good example about how to use pipes to get a different output, with a whole different purpose.
How to count how many processes each user is running in Linux
ps hax -o user | sort | uniq -c
ps will list the processes,
h will remove the header,
-o user prints only the user column,
sort sorts in alphabetical order, so
uniq can count each occurrence and show the number of occurrences instead of all the occurrences themselves.