I did OpenID early on in the site (nobody understood it), RPXNow/JanRain (more than we could afford for fewer features than we needed), and finally our own solution that does OAuth* for the various providers and Persona.

I love Persona. I want a Persona shirt and tattoo. OpenID was just a bit harder, but had nowhere near the payout that using Persona offers. The only burden of Persona is the auto-login/logout handling, which is a good thing in the long-run but in the short-run involves tracking down all your login/logout methods and making sure they all react properly.

*OAuth integration is a nasty mess of nastiness that I can't bring up w/o derailing this entire conversation. If you want to chat about that train-wreck, email me.

I also adore Persona. It took me two minutes to integrate on my Django setups the first time, and less than that on subsequent ones. Nowadays, it's all I use.

Not the GP, but I was thrilled with how easy it is to integrate. I have a little site that I'm putting together as a hobby, and it took me about an afternoon. Web development isn't my specialty, so if you know what you're doing you could probably do it in less than an hour.