The past few days marksmith and I have been working on implementing them into the LJ codebase. We are quite far along, have developed a strong backend that is already tied to the translation system (be happy timwi ;)), as well as have added them to almost every bml page that could take advantage of them. Right now we need feedback in terms of the crumb names, what pages are missing them, what should get changed, etc. They have, and will be, placed in the XColibur, Dystopia, BlueWhite, and Lynx schemes. While their placement has been discussed with xevinx it is not final and feedback is appreciated.
You can view the Zilla bug and patch here http://zilla.livejournal.org/show_bug.cgi?id=1668, requires an ljcomint install for some parts so I wouldn't recommend trying to apply it. You can however test it out and play with it on Goathack at http://goathack.livejournal.org:8064/. While they should be the same in each scheme please do try out the different schemes to make sure we haven't missed anything.
Thanks for your feedback and feel free to post any questions you may have.
Update: Whittaker has put this up on the test server now since it got checked into the CVS http://test.livejournal.org