What happens if the developers make a controversial change to the "standard" client? One criticism I commonly hear of Bitcoin is that it merely transfers trust from some sort of central bank or government entity to the developers of the main project.  Can anyone provide a clean summary of what would happen (technically speaking) if a large majority, small majority, large minority, or small minority of Bitcoin users opposed a backwords-incompatible change to the protocol via the standard client?  And does this "power to dissent" lie disproportionately with miners, and/or with major economic players like businesses and exchanges?
The power to dissent over changes that causes existing clients to reject a block does lie disproportionately with miners. Any change that causes existing clients to consider a block invalid is useless until the majority of miners update.

Miners who consider the block invalid will never attempt to build on a chain that includes any such blocks. So until a majority of miners upgrade, the longest chain will never stably contain a block requiring the update.

Once the majority of miners have updated, those running clients will pretty much have to update. Otherwise, they'll be stuck on a shorter block chain that won't agree with the more secure block chain.

The change would have to be pretty detrimental to key interests for businesses or ordinary users to be able to stand up to the miners. That seems pretty unlikely to me because there interests are pretty well aligned.