Banged out a good 9 miles around North London a couple of days ago, and my knee held up fine so I'm actually feeling reasonably confident it'll make it. I'm recovering a lot quicker now too: 24hrs after a run like that and the pain's pretty much gone. I'll be walking up every hill I encounter between now and the Marathon.
I've come to terms with the fact that I'm not going to have done the amount of mileage that I'd desired/is necessary. I've just got to get a few really long runs in and make do. Less than a month to go now : D.