Fixes a problem that causes "You don't have permission to do that" errors. It replaces the pluggable check_ajax_referer() with a safe alternative.
You only need this plugin if you are experiencing any of the perviously mentioned problems. If WordPress is working fine without it, then don't waste your time on this.
Note: WP 2.5 users do not need this plugin. It will not work.
Short answer: Yes. Longer answer: The replacement function provided by this plugin uses the same validation method as the original function. There is one difference and it has to do with encrypted cookie data. I suggest you have a look at the source code (it's commented) if you want to find out how it works exactly. The replacement function is no less secure than the original.
You may be experiencing one or more of the previously mentioned problems for a reason unrelated to AJAX or encrypted cookies. In that case, this plugin is unlikely to solve it. However, it could also be possible that the plugin just isn't perfect. In any case, it would be really helpful if you contacted me about your problem and providing the following information:
suhosin.cookie.encrypt(as displayed by the output of