I found a lot of information on melanosis/melanoma: Site on 'Iris Melanoma' with big ol' cat eyeball picture. Sounds bad, but they indicate most cases aren't serious. Eyeball freckles and 'age spots' seem common.

Floaters are inside the eye. They're gunk that floats around in the fluid inside the eyeball. I used to get a lot more floaters than I do know, and I'm not sure why. Maybe I just can't see them anymore.

Floaters are also what Cluin mentioned, which is gross, but funny. If you've got them in your eyes, you've really pissed off someone. I'd advise exhaling through your nose when they flush.

Floaters are also those etherial types at folk festivals that are really into the music (or the brownies) and just sort of glide around waving their arms and smiling a lot. If they're off on the sides, they really aren't a problem. Floaters have mostly been replaced these days (at least at the festivals I've been to) by people on cell phones.