If you have the one with the ranch dressing, it's actually lardier than a burger.
I'm sure I read that on the internet, so it must be true.
Edit: I did! I did! [link|http://www.associatedcontent.com/article/44895/are_mcdonalds_salad_dressings_healthy.html|clicky].
If I need food on the hoof, I'll head for Subway where I'll have the more-or-less fat-free chicken teryaki with all the salad and no sauces or dressings. Twas a revelation, that sarnie.