This seems to be an issue that will divide opinion down the middle. I see pros and cons to having kcal values on menus - but in general think it's a good idea to educate people as much as possible. I am very calorie aware - but I know many overweight people who genuinely significantly underestimate the calorie values of foods - so this would really help them to make more informed decisions. For those who would not like to see that info when eating out - I believe it would be entirely feasible to have 2 menus - 1 with values and 1 without and it would be the diner's preference as to which they see.
Most importantly however, in my mind, is the fact that this would actually put pressure on food establishments to consider more carefully the food they're producing - I strongly suspect many cooks/chefs have no idea of the imapct of the half pound of butter they use for flavour in many cases. This in turn may encourage them to look at healthier ingredients and cooking styles (for fear of poor sales on high calore foods) and this can only be a win win situation.
As I've said at the top here - this is an issue that definitely divides opinion. I'd love to hear from you - would you like to see calories on menus?