If you're a fan of Gazmik Fizzwidget's addons (including Feed-o-matic, ReagentCost, and Linkerator), you'll be happy to know that he's already jumping on top of patch 2.4, and in fact he's working right now on a beta of one of his most popular addons, Hunter's Helper. You can download the beta over on WoWInterface -- it won't work so well under WoW 2.3, but it's designed to be taken out on the TTR (or the PTR, if that comes back before the patch drops), and tested out.
Since it's likely that the patch will drop tomorrow, hopefully Fizzwidget has worked out most of the kinks. But it's awesome to see an addon developer ready to go for a brand new patch -- it's too bad that Blizzard hasn't been more proactive in helping these guys out with distributing their new versions around a big patch. Maybe once the Armory has gotten to a point where it's serving all the needs Blizzard wants it to, they can start working on an official third-party addon site.