Hey Matt,
The second issue is that of units.
Aaaahhhh... ...found this as well after checking this a bit more. Sometimes it's a bit hard to not get confused by the yt codebase :-) I couldn't imagine that yt tries to convert the result into the right units... ...but it's a nice feature!! :-)
http://hg.enzotools.org/yt/issue/281/nyx-units-are-incorrect
If you wouldn't mind, it'd be very helpful if you could fill in a bit about what you know -- from a pragmatic point of view -- about the units in that ticket.
For the Particle-Plotfiles it is: x,y,z in MPc velocities in km/s/a (where a is the comoving a) masses in M_{\sun} bye /Steffen -- () ascii ribbon campaign - against html e-mail /\ www.asciiribbon.org - against proprietary attachments