Since the Track Pad Film is basically a clear sticker that is designed to allow you to still use your MacBook's track pad, application is pretty simple. Some people prefer to wash the heck out of their hands, while I personally just peel back the underside of the sticker and apply without ever actually touching the film. There isn't much to say about how well the film protects your track pad and mouse button: it's a clear sticker, so those two components are pretty well covered, as long as you applied them properly. 'Nuff said.
In terms of the performance of the actual piece of film that covers the track pad, I have a mixed opinion: for the most part, the track pad still responds fairly accurately. I'm a dual-mode notebook mouser myself - I can use a track pad or a USB mouse with almost equal comfort and precision, so I'm not one of those people who's dead in the water if I have nothing but a fingertip to steer with. However, I notice at random times that my trackpad accuracy momentarily goes out the window - for a stroke or two on the pad, it might pick up only half the normal distance the mouse would typically travel, or the mouse might get a little shaky on the screen, as if Mac OS X is having a hard time understanding exactly where my finger is and where I want the mouse to go.
Overall, if we had an official rating system on TUAW, I would give the Track Pad Film a 7 out of 10. It's a decent product that can certainly help protect one's track pad from dirt and general wear and tear, but this occasional drop in accuracy is a big ding for this blogging power user.
I found Track Pad Film in a Colorado Apple Store for $12.95, but you can also order it for your MacBook/Pro (including a version specific for the black MacBook) from Power Support.