$(document).ready(callback)idiom, I thought it was a great idea: not only is it readable as plain English,
grep(1)able (it is available as
$(callback)too, but I advise against using that in larger code bases, where you might need to dig up all references to it, at some time) and intuitive, it also lets you provide a different document object you are waiting for.
The first time I used it in the latter capacity I was a bit saddened to find that it was not quite that good yet; it always tests the same document that jQuery itself was loaded into. (At present time, meaning jQuery 1.3.2 and earlier.) The document object you pass isn't actually even fed to all the code that together implements the ready function.
As we needed it to do that at MashLogic though, my colleague Dave took to fixing it so it does indeed work that way, as per the jQuery ticket that has been sitting around for two years (from someone else that apparently wanted and expected the same thing), and I submitted a patch upstream. I'm hopeful it gets accepted for next jQuery release.
We even prepared a little test case that loads jQuery in an iframe and puts document ready callbacks on both itself and its parent window, which seems to work fine in all browsers and OSes we have tested it in so far.