My sister is
Penny (not
Penelope). Actually, her real name is
Leona Dale and she earned the nick
Penny when she was about 10 years old. You see, she'd change her allowance into pennies because it made her feel she had more money so her friends began to call her Pennies and then
Penny. Anyway, she intends to change it legally one day and she loves being called
Penny. It's funny, though,
Penny is 15 years older than I am and yet I think she sounds younger because the name sounds so sweet and youthful.
So to answer your question, I do like
Penny, but traditionalist that I am, I'd use it as a nick for
Penelope.
Can Penny stand on its own? That's up to the individual, I suppose.