Interesting, and good, ideas. I think they could be defeated by a well designed spam bot, but most (if not all) currently used techniques could as well.

I haven't used a screen reader, nor have I looked at their source code, but it did make me wonder if such a setup (with user invisible fields) might still be read by the screen readers (depending on how they convert the raw html into content for the listener).

If I ever get around to fixing my comment system on my blog (I don't really like comments... and thats probably why my current commenting system is passive-aggressive), I'll try implementing these ideas. Good link.