Also, "it should be 4 spaces" is a matter of opinion--everyone likes different tab widths depending on their preferences and monitor size.
http://www.mediawiki.org/wiki/CC#Tab_size
"you should make no assumptions" appears to support Chad's statement. However, I'm pretty sure that in reality, many people assume a width of 4. I've definitely seen funky tab-plus-space indentations that support that theory.