I do not know if this counts as a hint, but with the way Snow Leopard has compressed the apps, it seems it's no longer possible to look through certain programs, such as Finder and Dock, with the strings utility in Terminal to find new hidden settings.
[robg adds: To clarify this hint, you can still run strings - someapp.app in Terminal to dump the strings (and redirect to a file, most likely). However, in that dumped file, you won't find any of the hidden defaults strings. I tested this with the Display full paths as Finder window titles hint. While the hint itself seems to work fine in 10.6, you won't find _FXShowPosixPathInTitle anywhere in the dump of Finder's strings.
If someone knows how/where/if you can find such hidden prefs in 10.6, please post -- otherwise, I think we'll see many fewer such tweaks here in the future.]

