Russ Roberts is blogging about the multiplier again, and I encourage people to go look at it and comment. There is little of the "you guys are just doing it for ideology" or "you guys are brimming with hubris and scientism" that you often get, so he seems to be in a mood to really talk about the stuff. I already have several comments, and I think readers should jump in too, particularly with points I didn't speak to - like the mechanism involved.
I know I've addressed all of these points several times before on his blog, and God knows the big-shot Keynesian bloggers have addressed all of them. But the more you discuss this stuff the more it gets understood and worked out.
UPDATE: More thoughts from Russ here. This one is a little more head-smack-invoking than his last post, but he does pose a specific question to Krugman, DeLong, Yglesias, and me, which I'm going to try to answer tomorrow morning before getting my study on.