about cabooses

[torikoos]

I've read another topic about the use of cabooses. However, I don't live in the US so I don't often see a 'real' US train passing me , nor have I had that pleasure when I was younger. :-)
Are cabooses still used today, or only sporadically, or are these now all phased out?
If so, when did this happen, and until what year (when modeling a certain era) could you still get away with putting them on a train?
When did steel cabooses first get introduced?

Thanks, Koos