And it's not just salespeople, a number of early stage engineers at Zynga were cut out of their equity / options entitlements by being relieved of duty just before the IPO; "got to be in it to win it" clauses in their employment contracts enabled this.

Point in lesson, always make sure accelerated vesting (equity, options, bonuses) clauses for not at fault firing, retrenchment, redundancy are in your employment contract.