I was a big fan of OpenDNS dns service, but recently I found few bad things about their offerings. I strongly recommend to stay away from OpenDNS service.
All your search queries belongs to OpenDNS
OpenDNS redirects all your Google search queries though their servers. They captures your search query data and they forwards to real google.com domain. Here is a quick DNS lookup:
$ host www.google.co.in 22.214.171.124
Using domain server: Name: 126.96.36.199 Address: 188.8.131.52#53 Aliases: www.google.co.in is an alias for www.google.com. www.google.com is an alias for google.navigation.opendns.com. google.navigation.opendns.com has address 184.108.40.206 google.navigation.opendns.com has address 220.127.116.11
They may also do same for your email and other search engine.
OpenDNS is bad for server
Don't use them on your colocated server or vps server. They redirect web browser users or scripts accessing nonexistent domains to a page containing sponsored search results, ads, and a search form. The DNS protocol requires that a query for a nonexistent domain must return the "NXDOMAIN" error response. Here is a sample output:
$ host abcabcxyzxyz.com 18.104.22.168
Using domain server: Name: 22.214.171.124 Address: 126.96.36.199#53 Aliases: abcabcxyzxyz.com has address 188.8.131.52 Host abcabcxyzxyz.com not found: 3(NXDOMAIN)
This encourages spam as you will not able to filter out spam queries using their dns servers.
OpenDNS caching sucks
I contacted their support about my problem but never got any reply. Their server always returns two IP address for my nameserver:
$ host ns2.nixcraft.net 184.108.40.206
Using domain server: Name: 220.127.116.11 Address: 18.104.22.168#53 Aliases: ns2.nixcraft.net has address 22.214.171.124 ns2.nixcraft.net has address 126.96.36.199
I don't have 2 IP address for ns2.nixcraft.net.
I strongly recommend running your own dns cache server along with your ISP forwarding nameservers.
Thanks to ricko for pointing out OpenDNS issue in a chat room and elsewhere on the Internet.
Update: Fri Nov 5, 2010 by Vivek: OpenDNS no longer redirects Google search queries though their servers:
$ host www.google.co.in 188.8.131.52 Using domain server: Name: 184.108.40.206 Address: 220.127.116.11#53 Aliases: www.google.co.in is an alias for www.google.com. www.google.com is an alias for www.l.google.com. www.l.google.com has address 18.104.22.168
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