They are still great as first, general info about, however not that much about VOPs or attributes there (at least this was in 2014).
Back to VOPs, I think it's good idea to take look at Attribute SOPs first, Attribute Create, Promote and such, they are providing a lot of functionality that in ICE belongs to get data from certain location, things like getting the attribute attached to polygon for use over points. For small example related to curves or strands, at first look it seemed impossible to get ICE style of switching between point and strand attributes, or curve to point in H. Later I found options from Attribute Promote SOP (minimum, maximum, average, summary...) as probably fastest equivalent to array ops in ICE.
Now about understanding the global concepts of H, I think great help is to learn something about... well.. Maya and Maya nodes. In many ways, Houdini stands as an complement to Maya, with exactly opposite concepts and capabilities. Maya is totally 'flat node context', while H is precisely divided to SOP DOP and whatever, Maya hates topology operations while H is able to break anything at any time but all that in H is not so fast, so on.