IceCaptcha "works", mostly. There is a permissions error generated when trying to change the settings even as the primary administrator account. See a report here. Editing the source files does change the settings. One just has to wait for the cache to catch up. If you want support from the plugin author, forget it.
I would use this plugin only for my own sites. I would not recommend it to clients unless the author, or someone else, fixed that error.