I'm trying to capture that look you get on old typewriters, where parts of the letters are smudged and/or missing.

i want to know a good way to apply this effect to entire images in photoshop. I've been experimenting with various filters, but I haven't gotten what I'm looking for yet. (I need it for a project that i'm working on.)

any help would be appreciated.

http://www.free-typewriter-fonts.com/

Depending on whether the typewritten document is supposed to be a good copy or not, you might do things manually like placing two letters in the same spot, putting pen marks over mistakes, etc.

Courier is the best look when it comes to the old typewriter . I'll screw around and see if I can produce something. I did it by hand once, but it doesn't always come out great.

I started with the text, in New Courier, on a white background. I used the quick mask mode and drew a big blurry smudge where the faded part is, and also added or removed various letters from the mask using a smaller brush. Back to standard mode, I adjusted the levels to make the selection a bit lighter.
I duplicated the layer, and added some monochromatic noise, used 'blur more', adjusted the levels to make the noise on the white part mostly fade away, and set that layer to multiply and merged the layers.
I then copied and pasted letters onto each other, and various other touch-ups. I probably should've done this part first...

Well done

perfect. thanks!