I have been following this thread with interest. The first thing I did was to grab all the books I could, they all say that a wort should/must be cooled as quickly as possible, there was little information on why. So I thought a summary of what information I could dredge up may be of assistance.
The pros all involve convenience.
The cons are for potential harm to the finished beer.
No one has argued that the no chiller method improves the quality of the wort and several concerns about the potential for harm have been touched on so:-
There is the very real risk of infection, 5 years in retail and I know for a fact that some prepacked worts are infected. That the number of problems is so small it is a testament to the brewers and their hygiene standards.
Microbiological Bizarre: the ricks from really out there microbiological attacks (I.E. Botulism) appears remote, if it concerns you avoid this method.
Hot break isnt an issue, if you follow good brewhouse practice and get complete separation of hot break and hop detritus. To the same standard as is required for wort that is going to be chilled, before transferring to a storage container.
Cold break again not an issue; the only people who have to worry about cold break are those using poorly modified or 6-row barley (USA). All the commercial packages I have seen have had some sediment, but not enough worry about.
The presence of oxygen will degrade the wort. All care must be exercised to avoid hot side aeration of the wort. Using a filling tube that reaches to the bottom of the storage container, minimising head space and having a well closed container should help. Commercial versions are generally filled to capacity; the whole container sucks in as the wort cools.
Obviously the wort will require good aeration before the yeast is pitched.
This is for me the big potential drawback, sensitivity to DMS is genetic, I am not highly sensitive to DMS but some people can detect remarkably small levels. To minimise the formation of DMS from its precursors it is important to get the temperature of the wort down from boiling to below 80C as quickly as possible.
As with cold break, levels of precursors in the grain play a major roll in how much of a problem this is likely to be, again we in Australia are blessed with grain that is going to give us the least problems. However if you are using European malts this could be a mater of concern especially for the production of paler Lagers and Pilsners. There are some good links earlier in this thread on DMS formation.
The Catch 22, to get down to a temperature where the formation of DMS is minimised, you loose the benefits of being above pasteurising heat. As the wort you are about to transfer is now highly infectable it cant be used to ensure sterility in the storage container. You cant think you are working to sanitary standards be certain.
If extreme care is taken with hygiene and oxygen exclusion, there are benefits in this method. There will be the odd infected batch but on the whole I for one dont see any serious impediments to the no chiller method being an asset to home brewers.
A bit of thought about the type of beer being produced and the ingredients used with this method will minimise any problems.