In today's engines spark plug life is not much of an issue. Hard driving and high boost pressures can have adverse effects on spark plugs, but with general driving you should be able to get a least two years of good service.
For turbo engines we recommend using Platinum or Iridium plugs. These coatings definitely improve service life under these harsher conditions. If you're running more than factory boost, choose the Iridium plugs.
