well with regards to the lemon thing, one of my friends told me that her cousin decided they should rub some lemon juice on their faces - on my friend, it left her skin glowing and blackheads were less and her overall complexion seemed more even; on her cousin, it left her skin burning, bright red, patchy, dry and peeling!
I think the moral of the story is approach lemon juice with caution! Personally i will stay far far away from it, as i find even some skin care products containing small amounts of any kind of acid to be too harsh, let alone lemon juice which is essentially pure acid! It's also strong enough to bleach hair, teeth etc so i think you have to have some pretty tough skin to take it, even diluted!