In reply to Jamie B:
There is a related thread on "Bolts in the UK" that has opinions, including some of mine, that seem relevant to this discussion. Have a look at
http://www.ukclimbing.com/forums/t.php?t=554061 .
I think questions about belay and abseil bolts overlap, but are still often different questions. And I think the answers are subtle and vexing. I'm going to stick with belay bolts here, because that commentary is by itself already long enough.
I think any understanding of trad clmbing involves making do with what nature provided. Climbers have gone to extraordinary lengths to avoid or minimize the use of bolts, but they have not completely eschewed bolting. Although confronting and dealing with risk is an inseparable part of trad climbing, it is usually assumed that the belays will be good, at least on rock in non-winter conditions. Most trad climbers regularly confront the possibility big and dangerous falls on "relatively easy" ground, and many deal with analogous risks on very difficult ground. But most climbers do not fancy having the entire party pitch off the crag because of inadequate belay anchors. Consequently, at least in my experience, there has been almost no controversy about belay bolts placed at stances with no natural opportunities to use conventional gear.
But such situations are very rare. There are entire crags where the need for a belay bolt never occurs. The vast majority of trad climbs have features that allow for the construction of belay anchors without drilling. So lets put aside the tiny minority of cases where it is a bolt or there is no anchor at all. I think the current discussion is really about bolting belay stances that do not require bolts. These cases, and I believe they are a huge majority of the instances, are mostly about convenience, which is surely not one of the goals of trad climbing. The party can carry lighter racks, since they won't be using up six pieces of gear at each pair of consecutive stances, they can move much faster, since they don't have to set up and break down belay anchors at each stance, and they can quit at any time---there is zero commitment---using the bolted belay anchors to rap off without leaving any gear. They can also use the bolts to set up a top rope on the first pitch, thereby clogging up the entryway to an entire route.
It is not possible to seriously argue that needing less gear, being guaranteed quicker passage, and having most if not all the commitment eliminated doesn't constitute an extreme alteration of a route.
Every time these issues come up, someone says that you don't have to clip the bolts. This again betrays a deep misunderstanding of trad climbing. Building a belay anchor is a skill that eliminates certain dire risks. Confronting the risks dictated by nature and dealing with them is what trad climbing is all about. It isn't about tricks like going over Niagra Falls in a barrel. Once the bolts are there, the entire process of confronting and resolving the risk is gone and not clipping the bolts is just a dumb trick, interesting in some cases, when people thought the bolts were "necessary," but ultimately still a stunt.
Oddly enough, those who say you don't have to clip the bolts seem strangely hostile to the idea that they don't have to do the climb if it isn't bolted. They insist on a choice for others that allows them not to have to make a much more fundamental choice. Underlying this is something new, in my opinion: a sense of entitlement, that says if the climb nature made isn't suitable for me, then by god we'll drill it up so that I can be comfortable on it.
That sense of entitlement has been, historically, the very furthest thing from the nature of UK climbing. Those of us from other lands who look to the UK as a beacon of the best aspects of trad climbing wish you well in keeping the drill where it belongs, on sport climbs.