How to set default Window position and/or size?
In Terminal you can change the default window size from Preferences > Settings > Window:



You can also use window groups to set a default position and size for the window opened when you launch Terminal (but not for new windows opened later).



I use Sequential and Skim as alternatives to Preview and iTerm 2 as an alternative to Terminal. All of them have an option to open windows in full screen by default, and all of them have their own (pre-Lion and actually usable) implementations for full screen windows.

The sizes of Finder windows are saved in .DS_Store files and there are no default window size settings in com.apple.Finder.plist or anything. I use a script like this to reset the properties of windows:

tell application "Finder"
    if number of Finder windows is 0 then return
    tell Finder window 1
        set toolbar visible to false
        set sidebar width to 0
        set statusbar visible to false
        set current view to column view
        set bounds to {960, 44, 1920, 1076}
        tell its column view options
            set shows icon to false
        end tell
    end tell
end tell