For example, old versions of vipnode that are incompatible with new versions could yield errors on peering requests. We should penalize them lightly so that they're not super-recurring.

Ideas for penalizing:

• Reduce priority relative to something? Maybe probabilistic? (E.g. skip 50% of the time, incremented to 100% with each failure? Decremented over time? Too complicated?)
• Put a "timeout" on them so that they're not considered for 10min? 60min?

Penalty should be reset on reconnect? Or should penalty slowly decrease on each success?