So you mean to tell me that if I was able to develop something that looked exactly like Facebook, but called it Truthbook there would be no legal issue?
Utility Patents are difficult for Software. More likely able to protect the backend technology than the front end look and feel. You can probably design around any Design patents.
Copyright protection not likely applicable unless you directly copy.
Trademark protection is your best bet for protection if it is likely to confuse customers, but that might be a tough case to make.
Good luck with Truthbook!