I have a K&N in my KJ and I have checked my air tube after every dusty trail run we take and their IS dust in the intake. I do have pics from when I recently changed out my stock 03 intake for the later model tube style shown above. I will find them and post here later. Personally I Am done w/ K&N filters.
Funny (or maybe stupid) that I used to defend them even knowing what I was seeing in my intake on my KJ and a previous vehicle that had a K&N.  I am pretty much done w/ unproven claims from the aftermarket. From now on if they can't show me tested proof, I'll pass.
My black list includes:
Splitfire plugs (total junk)
Slick 50 (snake oil)
Most "Magic in a can" type additives
All those "Fresh air/ Hi-flow air tubes on Ebay, etc.)
and Now K&N filters. (there are more, just can't think of them right now)
In a clean environment, where you want/need a Full flow filter that will at least keep the bugs out, (race cars perhaps) I suppose a K&N is fine. But on a vehicle that sees dusty trails and dirt roads often, IMHO, they just are not worth it. Also, many race teams running them in bad conditions are also Often rebuilding engines to keep them at top performance anyway. So I guess a little dirt in the engine isn't so bad for them. My goal now is to keep my oil as clean as possible for as long as possible. So no more dirty air for me.
BTW, if anyone wonders what I think about the Amsoil air filters, I Will be looking at them and asking some questions on how Amsoil tested them and what Their goals were. Based on the chart linked above, they appear to be pretty balanced in the middle as far as air flow vs. filtering. Maybe needing cleaning more often though. I will report what I find out. BTW, If I don't feel they are Best or at least better than most, I won't run or recommend them. (though I do have one coming for my XJ for Moab so I will get a real world test then)
Also, one more thing, Amsoil sells Wix, Donaldson and Their air filters, so they are not biased against another brands filter IF they work well. Notice from Link above also that Wix tests pretty well balanced in the testing too. In any vehicle that I didn't run a K&N in, including my XJ, it had a Wix. (based on things I learned about them when I worked auto parts) I also dig the Wix oil filters too, FWIW.
Back to the topic.
IF you use a good air filter and can draw air from a cool location I see no problem with an air tube. A straight or at least smooth tube from the stock air box to the intake is fine too so long as it dosn't act as a heat sink as some metal tubes do. (though some will say the air isn't in the tube long enough to matter, I still want my intake air as cool as possible)
An air intake that can be isolated from the hot engine compartment air should be fine also if used with a good filter.
Ok, I'm spent now and my fingers hurt...so I'll shut up as usual. Perhaps my ramblings will kill this thread too? 
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