I only met Callum briefly in Melbourne in 2007, right after I stopped volunteering for couchsurfing, right before he started volunteering for couchsurfing. A brief encounter with Callum was enough to know you're dealing with someone very smart and special. Later we started opencouchsurfing.org and regularly communicated online. I was happy to meet him again last summer in 2012. He wanted to start a new project and we brainstormed a bit about this. We were both avid users of ping.fm. I think Callum actually got me onto ping.fm at some point in 2007 or so.