Everyone except the FIA and the stewards of the race thinks this is silly, including Mark who has pointed out several previous incidents of F1 taxi rides on Twitter. The top photo shows Derek Warwick hitching a lift. Derek was one of the stewards in Singapore.
Update: Fernando Alonso has pitched in with his own 'Taxi' joke. See it under Mark's tweets.
Further update: OK so I might have been hasty in the 'everyone but the FIA thinks this is silly' comment. Some people clearly think Alonso and Webber's actions were dangerous. I've posted the video showing the 'taxi ride' below for you to make up your own mind. I still think the misdemeanour judgement was over the top but you may not. Mark Webber clearly still feels aggrieved about it.