Stolly's suggestions raise the question how one should distinguish between 'runners' and 'walkers'? The only sensible metric seems to be expected finishing time (EFT) and hence the current system already implements selective grouping of 'walkers', i.e., people who are expected to take longer then some set time (n.b., I'm not saying that only people who didn't get grouped are runners, I'm saying that the current system produces a split into two sets of entrants based on their expected finishing time, call them what you will). Hence maybe the more interesting question is what time should grouping commence? With 7:30 groupings (at Cray & Park Rash) people with an EFT of about 12hrs30 would make it through. 7pm groupings would mean only people sub 12hrs would be ungrouped (<5 in general). My opinion is that the current times are too early, in particular the 7pm grouping for this year (although I understand that grouping wasn't enforced till 8pm at Park Rash leading to a people with EFT ~13hrs getting through). With pretty light conditions till about 10pm (=13hrs) I think a more reasonable EFT boundary would be 14hrs, meaning grouping at Park Rash at about 9pm, Cray 7:30 (n.b. these are estimates based on a handful of rough leg times I know, one should look through the records of the CPs and come up with better estimates of how Cray/Park Rash times relate to EFT)
Overall I'm not against grouping - in fact, I think it is a good idea in general - however I feel that changing the grouping times could improve the event, making it more of a race the whole way for a larger proportion of the field. Obviously there will be people who will treat it as a race rather then a challenge who will be taking longer, but well one has to set a boundary somewhere and as I say overall I'm in favour of grouping, it's just with the faster people covering the Rark Rash - finish section in <2hrs grouping at 7pm seems overly cautious. One could also go to the other extreme and ensure everyone gets grouped, however that raises the question where to group the front runners, unless the start time were to be moved...
On the racing vs. challenge theme, I also feel that a better system for 'time allowed' once grouping has commenced could be put in place, in particular should the early grouping times remain, as this again allows a larger portion of the field to have a race if that's what they want.

Just my thoughts. In general I think that everyone involved in putting the Fellsman on is doing a fantastic job, I'm very grateful they do, I once again had a great time and am already looking forward to next year (whatever the grouping times might be ).