For people who want an impartial survey of multipliers, see Patrick Van Brusselen, "Fiscal Stabilisation Plans and the Outlook for the World Economy". It's a useful antidote to the blogposts that cherry-pick multipliers from a given model to make a given point. The survey ranges over US, euro-area, and Japan; and structural macroeconometric models, DSGEs, and VARs.

The paper also takes a longer run perspective.

Figure 4 suggests lots of opportunity for econometric testing for trend breaks, difference stationarity and trend stationarity. For some of the reasons of why that debate would be relevant, see here and here.

In several past posts, I've been taken to task for using the CBO measure of the output gap (and the associated measure of potential GDP) [0] [1]. Some criticize the false sense of certainty that is provided by the official measures, since they are known to be revised as data comes in. Some criticize the measures on the basis the fact that the statistical methodologies (Hodrick-Prescott, Band-Pass) are divorced from a formal economic model. Some criticize the concept of potential GDP derived from a production function approach (i.e., thinking about the economy as one big production function associated with one big firm...). Arnold Kling's recent critique centers upon the idea that output is not homogenous, and we need different types of capital (and by extension labor) when the desired composition of output changes. Yet another -- not entirely unrelated -- perspective argues that when relative prices change