I ran into the same problem after doing a "apt-get dist-upgrade" where systemd was upgraded from version 208-8 to 215-5+b1.
Upon reboot, "a start job is running for Create Volatile files and directories" appears to run forever, though I must admit I had only waited a few minutes before pressing "Ctrl-Alt-Del" to reboot, which, thankfully, worked.
I have Ubuntu 14.04 installed on another partition, so I was able to boot into Ubuntu diagnose the problem on my Debian partition.
I am very glad to have found your posts, which gave me an idea where to start looking.
After learning more about systemd-tmpfiles, I checked out each of the "volatile" directories, and when I tried to do a "ls -l /Debian/tmp", it kind of got stuck.
I managed to pkill the "ls" process from another console, then proceeded to umount the Debian partition and ran e2fsck on it. Came out clean.
Eventually, I tried to use debugfs to list that /tmp directory, and also let "ls -l tmp" run for almost an hour and got some output. It turns out that my /tmp directory was filled with some 628,000 symlinks to /etc/cups/ppd/Xerox_WorkCentre_6015NI.ppd . I recalled that I was in a hurry to print some music sheets, and Debian all of a sudden just wouldn't print to my printer after my "apt-get dist-upgrade" run, so I had to reboot into Ubuntu to do the printing.
So, after collecting output from "ls" and "debugfs", I finally went ahead to remove the old bloated /tmp directory and create it anew:
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# rm -rf /Debian/tmp
# mkdir /Debian/tmp
# chmod 1777 /Debian/tmp
I am about to reboot to see if it solves my problem.

Perhaps something did go wrong during that "apt-get dist-upgrade". /tmp is normally mounted as a tmpfs, right? All those symlinks should have resided in tmpfs, i.e. in RAM, but somehow they ended up in my ext4 filesystem, so perhaps /tmp got umount'ed during the system upgrade, perhaps even during the systemd 208-8 to 215-5+b1 upgrade? (Or maybe not? Perhaps I didn't have /tmp mounted as tmpfs, which is the case in my Ubuntu installation). Oh well, I will find out when I reboot.

Hope this helps!
Anthony
P.S. Hurray! It worked! I am back in Debian now.

P.P.S. As for my printing problem, it turns out that my /etc/cups/ppd/Xerox_WorkCentre_6015NI.ppd permission got changed by something a few days ago:
-rw-r----- 1 root lp 21519 Oct 8 18:07 Xerox_WorkCentre_6015NI.ppd
-rw-r--r-- 1 root root 21275 Jul 27 02:49 Xerox_WorkCentre_6015NI.ppd.O
Hmm... I wondered what happened. My /var/log/dpkg.log shows that some cups packages was being configured around 18:07 on Oct 8...