UPDATE: The problem with the "Make replacements directly..." feature has been fixed in Pages 2.x and Keynote 3.x.
This work-around is not necessary for these newer versions (part of iWork '06). For those that upgraded to these new versions of Pages and Keynote, you may want to turn direct replacements back on.
Do the Following:
Add Pages to the list of applications in the drawer in Spell Catcher's Preferences window. Select it in the list, select the Interactive pane, Typing tab. Uncheck "Make replacements directly..." (i.e. specifically for Pages).
Do the same for Keynote 2.
Hover the mouse over the "Make replacements directly..." checkbox for more information about this particular preference.
The above is required due to a bug in Pages 1/Keynote 2.