i love OutdoorGearLab.com… i find that their advice is derived after putting a product through the wringer, and therefore usually consult the webpage before purchasing most items. they have this to say about hydrophobic down, although it’s not very conclusive:

Hydrophobic Down??
Hydrophobic coated down has the potential to radically address down insulation’s only drawback- its susceptibility to loft loss from moisture. Nano technology coatings claim to prevent down from absorbing water and allow it to dry out faster once it does absorb water. Hydrophobic coatings have the potential to make a very good thing even better. But how much better and is it worth the additional 10% price increase?

Our preliminary field testing has shown that treated down is not a substitute for synthetic insulation in wet conditions. Testing by one well respected company (that prefers not to be named) has shown a negligible difference between treated an untreated down in real world experiments, such as if the bag gets soaked, perhaps during a river crossing, does it dry faster and re-loft faster? Their testing suggests that it does not. Another concern is durability. Down is extremely durable: it’s able to withstand hundreds of compressions, wide swings in temperatures, and proper washing restores twenty and even thirty year old down close to its original performance. We aim to test treated and untreated down side by side in sleeping bags and jackets over the long-term (and then test the down fill power) to see if treated down reduces durability. OutdoorGearLab is also in the process of developing quantitative tests through dummy skin temp probes and thermal imaging that will compare the insulation values of treated and untreated down.