I know this has been stated here before, but in the light of the growing hysteria it bears repeating: The US Food & Drug Administration <i>clearly</i> states that cooking spinach eliminates all e. coli threat, and you don't even need to cook it for long.
Here's an except and a link to the FDA's e. coli FAQ page, which is informative about this and a lot of other questions, too:
<i><b>Can people cook the fresh spinach or salad blends containing fresh spinach?</b>
As stated above, the FDA is currently recommending that the public not consume fresh (uncooked) spinach or salad blends containing fresh spinach. However, E. coli O157:H7 in spinach can be killed by cooking at 160 degrees Fahrenheit for 15 seconds. If consumers choose to cook the spinach they should follow these cooking instructions and also remember to take steps to avoid cross-contamination of the fresh spinach with other foods and food contact surfaces and to wash hands, utensils, and surfaces with hot, soapy water before and after handling the spinach. </i>
Nationwide E. Coli O157:H7 Outbreak: Questions & Answers
That being said, if I ran a restaurant, or was a lawyer retained by a restaurant to protect it against risk, I'd probably err on the side of caution and pull it from the menu until this blows over.
But I honestly would not hesitate to eat cooked spinach, at home or outside.