I arrived yesterday to Italy from Kenya, where I read on the IAAF site about Ryan Hall. As I don't know well the guy, and his training system, I cannot say something precise about him. However, I can expound my opinion regarding relation HM / Marathon.
Half Marathon is strictly connected with the ability in 10000m, CAN BE connected, in the future, with the Marathon, but it isn't a real test for the full distance.
You can run HM at the speed of your Anaerobic Threshold, that can be about 4-5 mmol for athletes, well prepared, coming from shorter distances. That's means that, if you are able to use a good distribution of rhytm, more even possible, you can run without too much accumulation of lactate, being able to remove from your fibres IN REAL TIME the lactate that you produce. For a top specialist of 10000m, only increasing his mileage (and the length of intervals too) without reducing the speed, can be a very good preparation for a strong half. In my experience, for example, I coached Paul Kosgei to win, in the first HM of his life, WHM Ch of 2002, however he was not able, at that moment, to run consistantly longer than 25 km (2 years later he bettered the WR of 25k in 1:12:45). The same last year with Robert Kipchumba : he was able to prepare 59:27 in Rotterdam with 2 months of preparation, and the 2nd place in WRRCh in 20k, but this doesn't mean anything looking for Marathon, because his mentality is yet very far from a correct training for this event.
One thing is the ability running a fast HM PREPARING MARATHON : this is a very good mark of good shape and very good training. Other thing to suppose that you can run a very good marathon PREPARING HM : this is completely wrong.
So, I don't know if Hall has the attitude for running a top marathon or not. If yes, he needs time for moving, under psychological and metabolic point of view, to a correct training and interpretation of full marathon. If he wants to try that road, I can suggest to run a good (but not top) marathon in November, having the only goal to make an experience (looking for 2:10 / 2:11), also because can be interested, for him, running WHMCh in Udine on 14 OCT, and the best thing is to have 4-5 weeks between a top HM (prepared for HM....) and a Marathon, and a bigger Marathon at the end of March 2008, for having time to prepare Beijing for Olympic. But, in Osaka this year and in Beijing, we go to face a very bad situation, with temperature of 30/35 degrees, and humidity of 85/90 %. Those are not the best conditions for a not expert athlete. In those conditions, for example, I suppose that Kenyan athletes cannot be too much competitive.
On the other side, I can be sure that 59:43 can be compared, without any doubt, with a under 27:00 time in 10000m. My opinion is that Hall, looking to his palmarees in the past, can try to prepare a 10000m under 27:00 for WCh, running about 13:00 in 5000m. One thing that can be very positive for him is his ability in running alone : this is one of the most important attitudes for becoming a Marathon runner.
But US must have patience. Instead, I see always a lot of hurry, from media and fans, with your young top athletes, and this is the real main problem that American runners have to face. Before speaking of medals, give to your athletes time to grow. You cannot win without top international experience, and you can do it only using time, may be 3 years. Going to World Ch or Olympic, an athlete must be IN HIS WORLD, being AN ACTOR, NOT A SPECTATOR. Too many times, an excess of pressure provokes bad results, destroying self confidence for long time. Don't do this mistake : low profile is the best way for becoming a top champion.