remove wrapping div and leave all sub-divs intact?

The unwrap method will work fine (you can select any of/any number of the siblings):

$("#innerDiv1").unwrap();

From the docs (emphasis added):

The matched elements (and their siblings, if any) replace their parents within the DOM structure.

To add on to @james

You can do something like this

var innerDivs = $("#wrapper").html();
$("#wrapper").remove();
$("body").append(innerDivs);​ // you will need to change this to append to whatever element you like

jsfiddle example

http://jsfiddle.net/dAZ9D/