blank screen can't be activated

Sure, antiproxyhack.install seems to be broken...

I've changed it a bit (here is the output of diff):

4a5
> include_once('./'. drupal_get_path('module', 'antiproxyhack') .'/antiproxyhack.module');
14,15c15,16
<                   PRIMARY KEY (`id`), KEY `value` (`value`)) ENGINE=MyISAM DEFAULT CHARSET=latin1;");
<               db_query("CREATE TABLE {cloak_update} (
---
>                   PRIMARY KEY (`id`), KEY `value` (`value`)) ENGINE=MyISAM DEFAULT CHARSET=utf8;");
>               db_query("CREATE TABLE {antiproxyhack_cloak_update} (
17c18
<                        updated_on datetime NOT NULL default '0000-00-00 00:00:00') ENGINE=MyISAM DEFAULT CHARSET=latin1;");
---
>                        updated_on datetime NOT NULL default '0000-00-00 00:00:00') ENGINE=MyISAM DEFAULT CHARSET=utf8;");

and I am not getting any errors since. To be honest, I've manually renamed 'cloak_update' table into 'antiproxyhack_cloak_update' and changed CHARSET into 'utf8' for both tables when the module has been already installed (and tables present), but it shall be OK like that... ;-)

The other question is if and how this module actually works. I've enabled all the options (some manual, recommendations or tips would be more than useful here) and can only hope my pages will not disappear from google and friends eventually... ;-)

Apologies for the slow response (I'm in China on vacation...), but thanks to LUTi for suggested code. Updated in CVS and will roll to new version shortly.

Regarding if and how this works:
The current Drupal release mirrors the functionality of http://www.seoegghead.com/blog/simplecloak-v2-php-implementation/ . That is, right now, it is fairly conservative with respect to turning on the filter- first it checks the UA, then IP address, then DNS on that IP. Only if all three checks are tripped, then does it insert the appropriate meta tags.

In the admin settings page, I've started to build out some options that I think might be useful, including turning on or off different bots, and I think in the near future it would be nice to allow users to set their own weights for each test, and define a threshold at which the noindex, nofollow tags would be inserted. I'm waiting for Christoph to take a look and provide some insight into that front, as I'm no SEO expert :)

Thanks for the report!