intertwingly

Re: point #2... let's review the definition of idempotent.  The methods GET, HEAD, PUT and DELETE share this property.  Yes, DELETE is idempotent.

As for #3... let's change the example slightly... for every query, your account balance is debited ten cents.  In other words, a scenario where one definitely incurs an obligation in return for the response.

Note: my real goal with bringing up this discussion was not to rehash RPC vs REST, but to establish that this is not a simple black or white issue.

Meanwhile, for those who haven't seen it, there is a fascinating discussion going on in the comments to my original blog entry.