Hey, our studio went thru a similar experience, where we shut down for 1 & 1/2 month just to study houdini. Before that I had been collecting video / pdf / sample files from the net so we had enough material to study. The best sites were:
www.buzz3d.com and
http://sidefx.vislab.usyd.edu.au/. [sidefx.vislab.usyd.edu.au] Most of the video tutes are a few versions old, but it doesn't really matter as most of the changes are easy to figure out (besides, it forces you to think and problem solve!).
There's also some good stuff around the net, do plenty of google searches and you'll find gems such as this:
http://cade.scope.edu/courseware/notes/houdini/index.html [
cade.scope.edu] for instance.
Obviously the two main houdini forums, this one and odforce is of great help too… searching in the archives usualy solves most questions.
There's also the mailing list archives, at:
http://www.sidefx.com/mailarchive/ [
sidefx.com]
Oh and one last thing, there is now a gnomon dvd that just came out. Lot's of good stuff in that as well.
Cheers,
Peter