[whpalmer4]

Well, you've actually got exactly the statement you need to do what you want. The tricky part is getting your hands on the selected item!

Here's a sample script that will append a string to the notes field of the selected items. Note that it does not drill down into contained items.

tell application "OmniFocus"
	tell front document
		tell (first document window whose index is 1)
			set theSelectedItems to selected trees of content
		end tell
		repeat with i from 1 to count of theSelectedItems
			set selectedItem to value of item i of theSelectedItems
			set theName to name of selectedItem
			set theNote to note of selectedItem
			set theNote to theNote & "
This is a note inserted in " & theName
			set note of selectedItem to theNote
		end repeat
	end tell
end tell