Think 'share of wallet', not 'share of market'

As the reviews for Seth Godin's new book start trickling in he decides to post his list of 'what every good marketer knows'. Each of the 30 or so bullet points is worth absorbing but the one that stands out for me is this -

- Share of wallet is easier, more profitable and ultimately more effective a measure than share of market.

How many business plans mention share of wallet? Time for a rewrite.