Thanks to all that offered help with my SxWiki problem.  It was indeed the User Agent.  I was able to get around it by adding this line to the _curlDo() function:

curl_setopt($ch, CURLOPT_USERAGENT, 'JaGaBot (using SxWiki 0.1.0)');

... just in case some other unfortunate soul runs into this problem.

Thanks again!

- Jason