The latest stable version of udev in prtage is 030. Since udev is the successor of devfs (at least for me) I would be nice to have a newer version stable. Since you're the main developer of udev and the maintainer of the gentoo udev ebuild you certainly know best, which version to consider stable. I run version 039 here on my desktop and laptop (both x86) and I didn't have any problems.
I will bring "stable" versions forward as I see fit. Right now there's still some issues with the current unstable versions (see the linux-hotplug-devel list for details.)
Cool. Hope that will be soon! ;)