I read about the K&N filter a bit when I was contemplating its use in my Pilot. There seems to be a trade off by using it in that the filter does allow more airflow, but then it allows more dirt in as well. So, with the former, you get the benefit of more complete combustion in the chambers which can translate into better performance and mileage, but with the latter, it can mean that more contaminants can enter your engine. At least that seems to be the consensus among people who seem to know more about cars than I do.
If you know how to use newsgroups, check out alt.autos.honda and rec.autos.makers.honda. I posted a question about Mobil1 oil and the K&N filter in there. Seems, if people had to choose one, they'd choose the oil, instead of the filter. You can also wash the K&N filter and reuse it, which I found very surprising.
Also, there are two types of K&N filters you can use. The ones that go into the filter casing, like the OEM ones, or you can use a cone shaped ones which will then require a whole new air intake and etc. From my understanding, you won't see much of a difference at all, with the one that'll go into the filter box.
I just didn't wanna take the risk of having more contaminants than neccessary, so I scrapped the plan of using the K&N filter. I do, however, plan on using Mobil1 once I surpass the 20,000KM mark. I called up all the Honda dealers in town and they all said to wait until about 20,000 - 25,000KM mark before I started using the synthetic oil. The reason given was that the seals, valves and other parts of the engine needs proper time to be set and sealed and if I were to use Mobil1 too soon, since the oil's so slippery, I wouldn't be giving my engine the chance to do so.
The dealer very close to my place let's customers bring in their own oil for their oil change, so, I plan on using the synthetic when the time comes. I weighed the pros and cons for both and using Mobil1 seemed to provide clearly more cons than pros but K&N filter wasn't so to me.
Again, my conclusion and decision was based on what others told me through those newsgroups and what I read upon the subject matter.