In the last 4 months, university holidays, I've been eating a fair bit of mickey D's(about 4-5 times a week) as it is about 10 meters from my desk at work, so I'd been eating it out of convenience.
My weight has remained the same(86-87kg), which is good as I'm a weight class athlete, my training has been going the same(good), and I've been feeling the same(good).
Now all the fast food probably isn't that great for my long term health I'll admit, but its' really not that much, and I think aslong as you don't go nuts with it, it can form part of a great strength building diet, and even a part of a relatively healthy one too if you manage it well.
I'm ceasing fulltime work next week and going back to study, so I won't be eating much fast food at all then. But I don't think it's all that bad, especially for somebody trying to gain strength and bulk.