The Wall Street Journal has a good chart shows the increase in the number of short term tax provisions in the tax code. Today, there are over 140 tax provisions that need to be renewed each year up from a dozen at the end of the 1990s.
A problem with the increase in the number of temporary measures is that they represent a source of uncertainly for taxpayers. Basically, they never know whether or not an extension will be granted the following years and whether their tax will go up or stay the same. At the same time, I suspect that some of the temporary measures are perceived as long term measures as people assume that they will be extended for political reasons. Another problem, I see with these temporary measures is that, even if everyone knows that they will likely be extended, they are used to trade votes in the same way as earmarks are. Finally, I think a lot of the temporary measures are not made permanent from budget reasons, and hence they are used by lawmakers as a budget gimmicks. It’s the way to get the spending or the tax break you want without having it be scored in the long run and without having to make the tough budgetary choices that need to be made.