There is a lot of debate about this. None of us wants the responsibility of telling you to do the wrong thing, of course. The engine is an interference type, which means that if a belt breaks it is highly likely that the engine will suffer serious damage as a result of moving pistons contacting non-moving valves that protrude into a combustion chamber. Other posts report repair estimates of several thousand dollars as a consequence, usually enough to justify installing an entire replacement engine. (Perhaps ironically, if the replacement engine comes from a used vehicle, it is recommended to change the timing belt on that engine before installing it.) So it is a justifiable expense to change the timing belt preemptively to avoid a potential catastrophic loss of money (and time).
Usually, when the timing belt is replaced it is a good time to replace the camshaft and crankshaft oil seals, the water pump, and the automatic tensioner/pulley and idler pulley. Most people replace the water pump, but many choose not to do the tensioners and/or oil seals on the first timing belt replacement if they seem okay. This accounts for some of the cost variability among different shops.
I changed the timing belt (+ water pump + tensioners + spark plugs) in our 2001 model at 125,000 miles a couple months ago for a parts cost of $400, but it took me more than 9 hours. (Estimates from local shops/dealers were between $700 and $1000). Contrary to what others report here, the old belt did not look new, it was drier and more flexible than the replacement belt, and there were some strands sticking out of the middle layer of the belt here and there. Also, my crankshaft oil seal was leaking, though not onto the belt. So replacing the belt in my case was probably the right thing to do at that time, but one never knows.
Based on the information in this forum, belt failure is very rare at lower mileages, but the effect of time is hard to judge. If you are in a mild climate you should be able to go much longer on your belt than someone who lives in a desert or winter climate. But belt life can also be shortened by a coolant or oil leak, or exposure of the belt to the elements through leaking or damaged timing belt covers. Without inspecting the belt you cannot really know if this could be happening.
I'd say, if an inspection of the belt (by looking under one of the upper timing belt covers) reveals that the belt is not dirty, oil- or coolant-soaked, and there is no obvious clicking noise from the pulleys, and you have no coolant loss or cooling issues (which could result from a worn water pump), you could probably safely wait at least a couple years before getting the belt + water pump replaced. If you live in an extreme climate or are risk-averse, just get them replaced now and sleep better at night.
