Rape girl confession caught on camera :
www.cphpost.dk/component/content/48436.html?task=view
It's also not neccessary to film oneself having consenting sex to prove that it was. You could put your hidden cam in your hallway so that your partner's smiling face is recorded as he/she leaves your bedroom.
Or, if you have the money, install security cameras at the entrance of your property.
Regarding proving that you were at place X and not Y on a certain date and time - I guess there must be applications for smartphones with GPS that will do that for you now?