Well, I actually “work” in this field (I’m a grad student in planetary geology). So maybe I can answer a bit.
The main reason we haven’t gone back since Apollo 17 was the lack of interest among the American people. Folks found it novel at first, and we proved our “superiority” to the USSR. But then it bored folks and people found it a waste of money. It was very expensive then, much more so than any solar system mission going on now.
We certainly have the technology to get back there, and we don’t need the Saturn V. Folks are looking into a trip to orbit in a vehicle like the shuttle and then launch from orbit. But this is all very much on the drawing board. We are lacking the very important money.
The president’s address, although not really financialy backed, has stirred furvor among space scientists, and they are planning missions that fit in with the president’s agenda.
However, a lot of scientists feel robotic missions are a lot more worthwhile and cost efficient, so active planning still involves this type of mission. For instance there is a mission in development to return samples from the far side of the Moon (South Pole-Aitken). This is robotic. My advisor is involved in a mission to deploy a set of seismometers on the Moon. This will give us invaluable information about the Moon’s interior structure.
To get more information about the topic of people returning to the Moon from people that are loud and respected voices in this field, check out an excellent book by Paul Spudis called “The Once and Future Moon”.
Also try a Google search for some of the well written rants by Harrison Schmitt (the last man to set foot on the Moon , and a geologist) proposing our return to the Moon. Schmitt is a big proponent of mining He3 from the Moon and returning it to Earth for energy purposes. He believes we need humans to do the mining.