tip #23948: if you see some sort of major obstruction (big pothole, roadkill, etc) ahead (especially if you're taking a pull at the front) call it out, or at the bare minimum use some sort of hand gesture (even better: do both)! And don't make any sudden moves.. swerves, sudden braking, etc are going to get amplified as they move back through the line.

But yeah, I wouldn't get too close to someone whose skill level is unknown. I'm quite comfortable riding 6" off Mike's wheel at speed, but that's only because we've ridden a lot together for extended periods of time.

As for Lordfoo's howto, it's a pretty good starting point. "Go easy on the brakes": I would actually advise trying not to use your brakes at all. I'm quite comfortable modulating my speed just by using wind resistance... just sit up a bit or pull out of the line slightly for small speed changes.