Orthotics and long distance running?

I've been regularly exercising since Jan 2010, kind of a New Years Resolution, started out to lose weight.  I'm down 35 lbs, (from about 200 lbs, male, medium build, 5'10") and want to lose about 10-15 more.

I've had orthotics (fitted by a Podiatrist) since spring 2008, to try and alleviate chronic (but mild) Plantar Fasciaitis.  Until the last few months, I hadn't run more than a couple miles with them.  Since Jan 2010, I've been losing weight, which started by mostly swimming, then adding in bike machine work along with spinning.  I noticed I could work in some running, since I was only doing it a couple times a week, but now it looks like I can do much more than that without PF problems.

I just registered for the Philly Marathon (doing the half), on November 21.  I ran 9 miles a couple weeks ago, and felt pretty good, except for the last mile, when my feet started to feel it.  I'll admit I hadn't ramped it up too much.  But 6-7 miles now is no big deal.  I'm using the half-mary as a gauge for trying a HIM next year.  The swim is not an issue, nor is the bike (at least to complete them).  The run for me will be the most punishing.

So my question is about these orthotics.  Is it generally OK to run long distances in them?  I would imagine suddenly changing to something else, then running 13 miles would be worse.

Thanks
Ted