Blocking by user agent if ip doesn't match

[karabaja]

Thanks everyone for being so helpful. I've ended up applying Igor's
suggestion. 
But I've dropped this line as I wasn't sure what to do with it:
"~(?i)(Purebot|Lipperhey|MaMaCaSpEr|libwww-perl|Mail.Ru|gold crawler)"
1;

I am guessing it can be used if I want to match more then just google's
user agent. But in any case what I did worked very nice. 
I tested it using Firefox user agent and I got forbidden page, then
tried adding my ip to geo bit and I was allowed. 

And there is lot less "google spiders" on our site now, and all of them
have ips I added to allowed list. 

Thanks again for fast and great advices. 

Since I am a noob when it comes to Nginx and now that I know I can get
some help here I am sure I'll have more questions :)

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,202715,202770#msg-202770