I know passengers who turn up at last minute may feel harshly treated by having boarding denied but have also experienced waiting in a fully laden 747 at SIN whilst a lady was running to get on board at last minute. Suffice to say all the surrounding passengers were extremely annoyed when the captain came on the PA and avised that due to the late passenger we had lost our slot and would be delayed another 90 mins. After a long trip from LHR all I wanted to do was get home to MEL and daresay the other passengers echoed similar sentiments. The airline would have been better off having 1 unhappy customer rather than 400.