I only add people to my "friends" when they ask to be. Some may not want the automatic up-sized pix, for example. I also never add anyone who specifically states being under 21y.o. since I cannot be privy to the legal statutes everywhere.

All the best.

The friend's list is more a vehicle allowing you to keep track of people you like more than it is for making friends. I have numerous people on my friends list that have never responded in kind and I don't imagine they ever will. On the other hand, I enjoy checking out their pictures on the "Your Friends Recent Uploads" page.

Some people don't want to use the Friends feature; others may only befriend certain types (sex, race, age, etc.) and yes, it's crappy; but either way, befriending someone here is a compliment from you to them and doesn't need to be responded to.

Enjoy the friends you have and don't worry about the rest. It's their loss, not yours.

I think 1XSpurt gives some very good advise, in regard with reminders and permissions.

And if they still don't react after sending a reminder:

To delte a member from your list, selct the box infront of the particular member and then press the 'Remove Selected from Friends'-button on the bottom of the list.