Confirmed, Arch Linux x86-64, systemd 197-4. I wasn't able to get an strace but in my case it wasn't a sustained problem. My fan kicked up I wondered what was causing it, pulled up htop and the journal was at 99% CPU on Core 0. Stayed like that for maybe 20seconds, then dropped back to normal.
All I was doing was web browsing with Chromium and Rekonq.
I find it odd that it hit 100% then eventually went back to normal, is there anything the journal does that should peg the CPU that hard? Or does systemd monitor the journal for hangs and restart it? (Did it hang, hence 100% cpu, systemd detected it, killed the journal and automatically restarted it?)