After talking it over with some of the other developers, it is becoming increasingly clear that YT is getting a bit unwieldy in its current organization scheme. Over the next couple months we're going to explore new ways to lay out the package structure, which will ultimately result in something with names that might have more meaning to a user, rather than the (admittedly) obtuse names that make up subpackages as they stand right now. (I honestly do not foresee any changes in the near future -- it is rather more likely that any changes would occur sometime in late December or mid-January.)
To that end, I am writing to encourage everyone to start using (or continue using, if you already are) the following idiom for gaining access to YT:
This will import into your local namespace all of the main objects one typically needs within YT, as well as the (current) subpackages 'lagos' and 'raven.' This idiom will be future compatible, and as such if you are using it now, your scripts should not have to be changed once we reorganize. Of course the 'iyt' entry point will be updated appropriately.
The reason for the change is a happy one -- we are currently getting more and more contributions, of both analysis pipelines and new means of data exploration. Right now, the import structure is rather sticky, which makes it difficult to import individual subpackages as well as deal with cross-subpackage imports, but with a suitable reorganization this will be addressable. (We're looking at lightcone generation, halo analysis, profiling of finely-grained timeseries data, rotating slice movies, and on and on.) Dealing with this head-on will help facilitate future contributions.
So, the summary: tons of cool stuff is coming (from inside and outside of the main dev team) and to accommodate that stuff, we'll have to move some things around, but if you use "from yt.mods import *" you should be set.
I definitely welcome any comments or suggestions!