According to an interview to promote his perhaps-last movie Contagion:

Mr. Soderbergh was speaking last month in his office space-cum-painting studio in the Flatiron district of Manhattan, where, having announced his imminent retirement from directing, he will soon be spending a lot more time. Propped against the walls are some of his recent pieces: a pair of striped canvases in red and gray hues and a portrait of the abstract painter Agnes Martin. Mr. Soderbergh, 48, sounded matter-of-fact about the career change. “I’m interested in exploring another art form while I have the time and ability to do so,” he said. “I’ll be the first person to say if I can’t be any good at it and run out of money I’ll be back making another ‘Ocean’s’ movie.”

He's a reverse-Schnabel! And also, very honest. Much as we're like to see him succeed, Ocean's 13 did leave some unanswered questions to be explored in a sequel (e.g. Why do people that rich need to keep stealing things?).  Anyway, it's a win-win!