One of the arguments used by the supporters of Measure 49 (about which more later) was that owners of Oregon farmland shouldn't complain about being downzoned for exclusive farm use, because they got the benefit of special assessment of their farms for property tax purposes in exchange for being downzoned. The argument had one big flaw, which is that if the land is zoned for exclusive farm use and used for farming, then farming is likely its highest and best use and therefore fixes the value at which it will be assessed, special use program or no.
The argument intrigued me, however, because it suggested that the special assessment for farm use (currently in ORS Chapter 308A) was a quid pro quo for the limitations of the statewide land use program, so I did a little digging into the history of the special assessment program.
Actually, Oregon gave a tax break to farmland years before we had statewide land use planning. This 1999 paper (PDF) by David R. Brooks, then a candidate for a master's degree in planning at Portland State University, gives some useful history. According to Mr. Brooks, Oregon first considered specially assessing farmland in the 1920s, and enacted its first statute to that effect in 1961. (He says that all states have similar programs.) The purpose of the statute was to preserve farmland by offering farmers a reduction in their property taxes if they kept their land in farming. People who wanted farmland for non-farm purposes (whether martini farms, industry, or urban sprawl) would pay more for the land than it was worth to farmers, and the farms were being tax-assessed at that higher value. So the statute said that if the owner of land in an exclusive farm use zone used it for farming, the land would be assessed at its true cash value if used for farming, without regard to other possible uses. (But see below for an exception.) The program was substantially revised in 1963 and 1967, in each case before Oregon had statewide land use planning. (Mr. Brooks notes that one reason the 1961 program failed is that it applied only to land in an EFU zone, but because Oregon did not require counties to adopt zoning, much farmland wasn't zoned at all and therefore didn't qualify for the tax break.)
The exception I referred to above is that farmland that's near the edge of town (in 1963) or close to the Urban Growth Boundary in an urban reserve (in 2007) has a speculative value higher than its farm value. The tax break means something there, but a good share of the benefits go to land investors rather than to actual farmers. (As you move from entrenched farming areas closer to the UGB, the percentage of land held by speculators, investors, and potential developers goes up.)
I don't think that this argument ultimately affected many votes on Measure 49. The "yes" voters weren't voting to punish those greedy tax-evading farmers, and the "no" voters weren't wrapped up in the philosophical flaws of this particular "yes" argument. Rather, Measure 37 passed because the excessive regulations of a few cities and counties produced enough outrage across the state, and Measure 49 passed because the excessive claims of a few lucky landowners also produced enough outrage across the state.