"Can opendns work as an unblocking service?"
It depends. If you're facing blocking measures with the default DNS service you use, OpenDNS may be able to help getting around such measures. But this is apparently not what you're thinking about.
"Does it show me up as logged in from another location?"
No, never. DNS is the phone book of the internet, not the phone lines. And same as with the phone, the remote side still sees your number (IP address), no matter what phone book you have consulted before to make the call.
"I want to use blocked services like Netflix. Does opendns cover that?"
As of my above explanation, no, OpenDNS (or any other DNS service) does not cover this. You'll want to look after a VPN service or a proxy service instead, not a DNS service.
"or is it only used for security?"
No, not only. OpenDNS is foremost a recursive DNS service, like a phone book, giving the numbers (IP addresses) for (domain) names, in principle the same as any other recursive DNS service. But it has additional features like logs and stats of your DNS traffic (your looks into the internet phone book), domain blocking and filtering, etc.
