For most languages there is a context assist that helps with currently active function signature.
For example, in Java, after typing function( CTRL+SPACE brings list of signatures and selecting a signature auto-fills parameters placeholders (in fact it does this when having just part of function name, in any event of selection from signature assist).
In FlashBuilder/Action script there even more intelligence, in addition to CTRL+SPACE there is CTRL+SPACE+SHIFT that shows the signature tool tip and highlights live where you are in the parameter list as you move the caret.
WebClipse/Ts only allows just selecting function name and puts it in the editor regardless of context. If one types ( and CTRL+SPACE after that, it just suggest all functions list again.
Would be very nice to have at least minimal parameter/signature intelligence in function/method context assist. Even just display-only tooltip with signature list on CTRL+SPACE would be helpful, because currently it requires moving the mouse to see the signature while typing the code.