I intended to elaborate on the captcha problems in the original thread, but since it has been locked, I have no choice but to create a new thread. I think it is very important that the SE designers understand that mathematics places very unique demands on the software platform.
In the original thread Jeff Atwood speculated that a browser/network config problem might be the source of the many annoying captchas that I face (e.g. over 20 in one recent few hour period). He added that this "barely comes up" on, say, StackOverflow. The reason for that is quite simple. Mathematics has much richer structure than most other fields of knowledge. It has much deeper levels of abstraction and a much, much wider web of interconnections between various subfields. I think it is very important when teaching to point out these interesting interconnections. Sometimes these surprising and beautiful links are precisely what spurs students to study mathematics. So I often pepper my posts with links to related topics, e.g. generalizations, specializations, cryptomorphisms, etc. This can trigger a network of edits to related posts - a flurry of quick activity which furiously tickles the captcha dragon's tail.
Often times when the captcha arises it seriously disrupts my thought process. When one is trying to keep a moderately complex web of math ideas in mind to perform some related edits, having to deal with a barrage of annoying captchas can force a mental "stack overflow", i.e. short-term memory overflow. Mathematical reasoning places great demands on the pattern-matching parts of the mind. Having to swap math stuff out of mind so to recognize some obfuscated captcha text can seriously hamper one's mathematical thought processes. Not to mention time constraints. On a few occasions captchas forced me to run out of (spare) time, so I had to return to my answer later - making it much more difficult to remember what I was doing (half a minute of captcha solving time can be the straw that breaks the camel's back when your girlfriend is dragging you out the door after ten minutes of "be there in a minute" ... not to mention my young niece who, alas, overheard my cursing not "captcha" but her beloved "Casper" - the friendly ghost).
Perhaps an analogy will help. Adriaan de Groot, a chess master and psychologist, wrote a famous book "Thought and choice in chess" which explored at length how the mind works in chess grandmasters. He speculated that grandmasters reprogram certain pattern-matching parts of the mind for recognizing chess patterns - similar to what occurs in mathematics. To disprupt the mathematical thought processes with captcha's is quite analogous to forcing chess players to solve a captcha if they make too many rapid moves in succession. Of course a chess gaming site with such captcha's would never succeed. An analogous argument holds for mathematics.
So, SE designers, could you please reconsider the captcha algorithm. I think it should be easy to eliminate the above problems without sacrificing the original captcha design goals.
Note: most of my edits don't show in the edit history since they are within the 5 minute window where edits are coalesced. So it is not easy to give specific examples that show how the captcha was triggered.