But as a reformed cell nerd, my beef with the diagram i linked to is that the structure is wiggly, implying that it is slack and flexible. Actin isn't. Whenever you see actin filaments in a cell, they're part of a structure that is either under tension, and so is made of long straight bits, or compression, and so is lots of short straight bits anchored to something.

EDIT Here is a lovely picture showing the actin in cancer cells growing on a glass slide:

https://en.wikipedia.org/wiki/Wikipedia:Featured_picture_can...

The actin next to the slide is red, and the actin on the top of the cell is purple. Around the edge, you have filopodia and lamellipodia, small compression structures poking outward from the cell. In the left half, you have stress fibres, tension structures anchored in adhesions on the bottom of the cell, concentrated near the edge, and reaching up into the cell body. I'm not certain what the little scribbles making up the crown on the cell's head (around the purple blob) are, but i think they're little flaps sticking up out of the cell which are involved in pinocyosis - compression structures like the lamellipodia. Bottom-rightward of the purple blob you can see a cell-cell junction, a sort of vague line with perpendicular stress fibres terminating in it. The little dots are probably associated with vesicles (not sure if those are in tension or compression, actually).