First Marathon will be during my first IM

With your ITB issue, bag the marathon.  No need to do it, especially with an injury issue.  It could set you back much further in your IM build for KY.

I knew I was going to do an IM distance in 2010, so I did a trail marathon at the end of 2009 which is really a different beast then a nice road marathon.  But either way I was glad I did it and the relentless hills laughed at me as they chewed me up.  There is no way I would've done an early season marathon in 2010, I needed to assure I got my tri training in for 140.6 miles and I think doing an early season marathon would've harmed me more then helped me. 

And think about it whats your goal for 2010, nailing a marathon or the IM.  I know what my choice would be.

Good luck with your recovery.

I "followed" the Intermediate plan for IMCdA and the long runs were fine.  I did a lot of extra running prior to and early in the training program because I did a 50-mile trail run 10 weeks prior to IMCdA.  I'd say the ultra did a lot more to simulate the late-in-the-day-"running" that most IM finishers (at least most of us 13+ hour finishers) than a stand-alone marathon would.  I signed up to work on the mental fortutude to keep moving forward 10-11 hours into a race day.  I took a week off running after the ultra with some riding (trainer) and swimming.  Even 2-3 weeks later, I could still feel some fatigue in my legs from the run (no real speed on the bike and not much gas to power up hills), but I think it worked for me. 

Now I did go into the ultra ready to DNF if I felt continuing would jeopardize IMCdA training.  (Risks included tendonitis/inflamation, a fatigue related fall or strain, and blisters.  None of which happened. ) 

A standalone marathon and the Ironman marathon are on two different planets with almost no relation to each other. Thousands of successful Ironman athletes have never run a marathon (raises hand, 7x IM finisher, would rather chew glass than run a marathon). A marathon does not punch your IM ticket.

There are other significant scheduling considerations as well regarding the insertion of a marathon into a triathlon training schedule.

Here is blog post with videos of my partner and I discussing a marathon in the off-season, but the scheduling considerations are the same, and even more serious, for any triathlete thinking of doing a marathon after about...January.

In short, don't do it.

As many of the folks above have stated a stand alone Marathon and an IM Marathon are two totally different animals. I have coached many first time IMers (100% Finisher rate ) and maybe 1/3 had done a Marathon prior to their IM races.

Aerobic fitness is aerobic fitness and it doesn't matter where you build it for it to be effective. A long run of 2-2.5 hours max is plenty and that is more for conditioning the joints and connective tissues to accept a pounding for that long rather than building run fitness. Just keep in mind the longer you run the more you are exposing yourself to injury.

As a side note, don't go crazy with the brick workouts either. Most people mistakenly think that bricks are what help you run better off the bike. Not true! Bricks are more to test your nutritional and pacing strategies on the bike. If you pace the bike correctly and  have a sound nutritional plan then running off the bike is a function of your run fitness after the jello legs go away.

We are  going to have to just agree to disagree on this one

A 56 mile bike followed by a 13 mile run in training is completely uneccessary. Again with proper run training the longest brick that you should do is a 50 mile bike at race pace followed by at most 8 miles (I usually don't go over 6) at AeT.

As far as IM bricks go......every single one of my athletes do a 5 hour bike/1 hour run brick at their race rehersal a couple of times during the final peak phase before the taper. After being on the bike for 5 hours using the nurtitional product of  your choice and the getting off and running an hour at goal pace you are going to find out pretty quickly if that nutrition is sitting well and if you paced the bike correctly.

People put way too much stock in bricks for long course racing. Short course is another animal because you only have 5k or 10k to get your legs going and get up to speed. For HIM and IM races it doesn't really matter if your first mile is slower while you get your legs under you and get you HR to settle in, there are 12 or 25 miles respectively to make up for any under paceing the first few miles.

Consider  yourself fortunate to not have experienced any nutritional issues, I find that is the biggest reason for poor performance over long course racing.

I agree with Brian on this one....this is a terrible idea. You are going to end up injured or worse, not to mention that every time you do one of these "Super Bricks" the recovery is going to punch a huge hole in  your training plan. You just don't go out and do a huge workout like that and go back to regular training the next day or even the next week.

The key to a good run off the bike at the IM or HIM distance is pacing and nutrition coupled with good run fitness. If you are doing quality long runs and you proper learn to pace the bike by either HR or Power and your nutrition is sound I can almost guarantee a good run off the bike. It is that simple and that hard all at the same time.