OmniFocus lets you set custom perspectives. The perspective I live in the most is one I made myself called “Today”. It only shows me available actions which are due plus any flagged items. What I like about having flagged items appear in my Today perspective is that sometimes I know a new action item needs to be done today but don’t want to fiddle with assigning a context or project or due date (especially when entering it via my iPhone or iPad). Thus, flagging the item is the quickest way to get that task into Today’s list.
Shawn has written extensively about Omnifocus on his own site, shawnblanc.net, and every single one of his posts are required reading for those of you out there who rely on Omnifocus as your "trusted system". In fact his entire site is required reading. So go. Now.