> ...Like it or not, many webmasters who insist on
> using visual CAPTCHAs (often in combination with JavaScript) are turning
> away customers. ..

And not just visually impaired people. I screw these up all the time
and my vision is fine.

> ....Logic puzzles,
> presented as simple text, are the approach we use most commonly, although
> Google's apparent ability to solve some of these does have us a little
> concerned.

These are no silver bullet either since language and comprehension
abilities start coming into play. The reality is that any test
designed to weed out the machines is going to week out a few humans as
well. The trick is to figure out how to minimize that number and then
identify who gets locked out so you can find another way to help them.

> I'm not sure it's ever good a good idea to insult your users, or your
> colleagues. I know that I've seen CAPTCHA's with the message that boils down
> to "to help us make sure you're really a human, please fill this out." I'm
> not disabled, but I am insulted by these messages!

Yer too sensitive. May as well be insulted that rocks are too hard.
Bots are a real threat to services. Once they get out of control,
systems can become overwhelmed, legitimate users get flooded with
garbage, and attacks can get launched which can get your site
blacklisted. Then all your users are hosed. It is easier than most
people think for pretty rotten scenarios to emerge.