Is there a limit to how many words will be revealed with the Letters From A Friend and Argneir's (sp) whispers? I KNOW that I haven't unlocked them all, but I've stopped getting both. (I haven't done anything to piss off Argneir.)

Edit your post.
Major spoiler.
And if you stopped getting them you probably have all of them.

no limit, afaik

Fixed and I don't have them all.

I only have 13 different words unlocked, and most of them aren't complete shouts. (i.e, Kyne's Peace. I only have two of those words...that's only one of my incomplete shouts though)

Must be a bug then, you should try checking UESP.

There's a lot of "shout" information at this link:

http://www.uesp.net/wiki/Skyrim:Shout

Hope it helps you out.

Good luck.

Womp. I think I might have a variation of that Argneir bug (except with the letters too).

I hope Bethesda fixes it.