In reply to GridNorth:
I think GN is right, there is a role for bolts for certain anchors in trad climbing, but it turns out to be exceptionally difficult to (1) do things "right," and (2) to keep the lid on bolting once you've agreed on some. If there is a moral to the tale, it is beware of the unintended side-effects.
Over the pond here in the Gunks, we've seen some of the issues play out. The Gunks are unique in being on a privately-owned (non-profit) preserve, (the Mohonk Preserve), which can and does make rules about fixed anchors.
It's a little more complicated than I'm making it here, but basically the Preserve bans bolting, except if done by the Preserve itself. That solves problem (2) mentioned above, but not in a way that can be imitated elsewhere.
One area of the Preserve, the Trapps, has substantial crowding issues. Moreover, although walking back down is easy, it also means a long round trip back to the base of the climb where climbers typically leave stuff. So over the years, a plethora of rappel anchors appeared, creating ugly and dangerous situations.
The Preserve decided to intervene and replace some of the highest-traffic anchors with bolts and chains. In retrospect, this was a classic mistake: do not let climbers intent on doing certain routes and descending from them determine the location of anchors by simply replacing the most tat-filled anchors with bolts. What happened is that the Preserve established bolted rap stations that sent descending climbers directly down popular routes, thereby creating more problems than they "solved."
Another aspect of the Preserve's mistakes in the original bolting was that they failed to mitigate environmental impacts. A number of trees on the cliff have been weakened and killed by rappellers, and the Preserve hoped to spare further destruction by getting slings off the trees. But slings on the trees weren't the problem, it was the soil compaction of climbers stomping around the trees while setting up rappels. So, when the Preserve put bolts right next to these trees, the result was to continue the real source of environmental damage rather than mitigate it.
Having learned from the initial missteps, the Preserve established a few more bolted rappel lines that, as much as possible, avoided climbing routes, and certainly the popular ones. The idea, which has not been fully realized, was to create a collection of descent lines for rappellers that would keep walking to a minimum and would not pit descending climbers against ascending climbers.
This idea might eventually work reasonably well, but not without a step the Preserve (perhaps for legal reasons) has not been willing to take, which would be banning climbers from constructing willy-nilly their own rappel anchors wherever they desire. So now we have bolts and pretty much the same plethora of tatty rap stations.
So, what are some of the lessons?
1. If at all possible, do not bolt belay anchors on ascent routes, because it will
(a) create two-way traffic on the route
(b) make it convenient and attractive for climbers to climb the first pitch and then set up a top-rope on it, monopolizing the climb and preventing others from doing the route.
2. If environmental impacts are important, think long and hard about
(a) what new ones the bolts will create
(b) whether the bolts will really solve the original ones.
Good luck, and when in doubt, don't do it.