Putting together the mockup of NetNewsWire with favicons it was interesting to discover how broadly the quality and format of the icons did vary.
If comments appearing on Inessential.com are an indication, people seem to like the idea. Although another possible trade-off occured to me, beyond the odd ugly icon.
The current method of the feedback used to indicate loading states might need adjustment.
Currently the loading/checking process is displayed nicely with colour changes in the globe icons as each feed in the list is updated. Presumably to maintain this feedback it would be necessary to not reveal the custom icon while the feed was updating. Even then the relatively subtle colour changes may be lost amoungst the column of brighter pixels.
One alternative solution could be changing the colour of the accompaning text to correspond with more than just the feed 'loaded' (black) and feed 'not loaded' (grey) states. Or perhaps to be more easily distinguished from the other icons, the loading states could be represented with that familiar rotating grey spinner.
This would probably mean simplifing the number of states currently used, but how many do we really need?