Question: I consider Facebook to have information that is personal and that I only share with close friends and family. However, in my new workplace I’ve been asked several times for my Facebook username and/or have been *friend requested* and I don’t want to sound rude by telling them that I don't want to add them as friends. 

Any suggestions on the way I should handle this?

Answer: 
My policy, when I was on Facebook, was very simple: Friends were just that, *friends*. I didn't add acquaintances, I didn't add every coworker, I didn't add folks whom I knew by sight but hadn't spent a significant amount of social time with. Period.

You don't have to respond to the request. Just ignore it, and let them deal with it. But you also don't have to feel bad about saying "Thanks, but no; I'm keeping work and personal life separate."

Ditto for any other social medium, unless you're in a situation where you're trying to do business via same... and then I'd suggest a separate account.
I have a simple way of dealing with that.
I have the fortune of having a really good relationship with my workmates, even with the senior one, but since i have a totally uncommon life style, i've decided to not disclose my free time with them.

Since we are Italians, we tend to create strong groups and ties with people we work with, so to not refuse them the friendship on fb, i have created a fake profile as decoy for them.
So my "real" profile is one with a nick name, the "official" one is one with my real name and surname.

I've found it really useful even for online privacy and other social network connection, namely Linkedin, and it also doubles as a self-promotion tool for my working life.

Remember: you'll never be "too much" safe online.