In Visual Studio—my main squeeze for many years—I can press Ctrl+F to immediately search for the identifier or string that my text caret is touching, or else the currently selected text if I have a selection. I can press Ctrl+Shift+F to search the whole project, solution, or other file sets. I like this.
In Xcode 3.*—my main squeeze in recent years—I could press Cmd+Opt+F to immediately search for the currently selected text and Cmd+Opt+Shift+F (a bit of a handful, but workable), to search throughout the project. I liked this a bit less than the VS approach because I first had to select some text, then search for it, rather than the IDE automatically picking up the current identifier for me if I hadn't selected anything. But it was fine.
Now in Xcode 4 I notice that there is a Cmd+E shortcut that makes Xcode "Use Selection for Find." But it... well it sucks bad. All it does--apparently--is to copy the current selection and paste it into the find box. It doesn't show the find box, so if the find box isn't currently shown then Cmd+E has no visible effect. Cmd-E does not actually invoke the search--it only copies the text. So now searching for an identifier becomes a three step process: select the identifier, press Cmd+E, press Cmd+F (or Cmd+Shift+F for project-wide search).
IMO, Xcode 4's three-step process is worse than Xcode 3's two-step process, which is worse than Visual Studio's one-step process.
My question: In light of this falling UI efficiency along with recent international events, is the world just going downhill and soon all will end in a fiery apocalypse in which the few remaining humans will be forced to retype War and Peace each time they want to search for an identifier?
ughoavgfhw offered the correct answer (above). Use Cmd+E on the selected text to begin searching with that text. Then immediately type Cmd+Shift+F to search the whole project for all instances of the text hit enter.
This is quite quick, consistent, and sensible. It's not as immediate as Visual Studio's single-stroke Find/Find-in-Files—Xcode requires two strokes rather than one—but personally the extra step doesn't bother me.