>>7
Yes when you only see it once it really isn't a big deal, but when you have to solve one every time you try to post it becomes a complete pain in the ass (imageboards, comments on blogs, comments on news stories...)

>>and prevent any IP or block of IPs from requesting too many captchas, and their job becomes a lot harder

You don't need to request a lot, only request one when someone conencts to your dummy site and put a timeout on how fast you spam particular sites...preventing lots of captcha gets is exactly equivilant to preventing excessive posting, so the captcha serves no purpose in this case

>>Ensure that the referrer is always your site

This does nothing, the server fetchs a captcha when it needs one and then once the dummy has solved it it then submits it... if it fails fail the dummy and try again, how exactly does a referrer do anything?

>>Only relevant to large sites.

One dummy porn site can service the spamming needs of many, many small sites. Large sites are not likely targets that will be effective, as they will put things into place that deal with them even after they get through (moderators deleting, saging, whatever). The ideal target is one that has an audience but isn't large enough to get hit often. Example: GNAA can spam slashdot all they want, but they will get modded down and dealt with quickly no matter how well they spam/troll/whatever

My point isn't that captchas are bad/should be done away with (which is a whole 'nother discussion), but that breaking them doesn't hurt them if it isn't disclosed