‘Sell in May and go away’ in 2013– history suggests it might be good advice

It's an old investment cliché that has long been trotted out as advice, though few take it seriously. Based on recent history the stock market adage 'sell in May and go away, buy again on Leger's day' might well be good advice. So in 2013 should investors sell up or ‘buy and hold’, and if so which funds?