In regards to picking Ajmal's doosra, it effectiveness is greatly improved by its disguise. He bowls with a scrambled seam so the traditional ways of reading it by the hand or the seam position are hindered considerably. That the main reason why he so difficult to pick is because he can bowl, both the doosra and his off break with the exact same action, so no one knows which way it was going to turn. Also his doosra doesn't turn a lot, just subtle movement the other way. especially in comparison to Murali and when it does turn too much it will miss the bat. so its not the amount of turn that gets wicket its not knowing when its coming.
Remember this ball was invented by Saqlain Mushtaq, and he had considerable success with it. but the problem he had was eventually he over-bowled this and most batsmen got used to it and generally picked it most of the time. they negated it and he was towards the end of his international career seen as a one trick pony. Ajmal uses the his ability to disguise to its maximum effect. There have been cases where certain bowlers were banned from bowling their doosra such as Harbhajan, Shohaib Malik and even Murali for a short period time. I know that Malik is still not allowed to bowl his as it illegal and more than 15 degrees. so if Ajmal is chucking why is still allowed to bowl it?
Bottom line, forget all the people who disagree and whether its chucking or not, until the ICC move to ban the doosra altogether, its a legal delivery. So just get on with it and play the ball.