reusable filters do let more debris into the engine when they are new. That is a fact. You can see light through them when they are new. They do get better at filtering over time though.
I have to agree that if you take a new K&N or Airraid or any other reusable filter new out of the box, then run you vehicle with clean oil. The next time you change the oil and do an oil analysis you WILL see more debris in the oil.
Once the filter has a chance to get sufficiently dirty though it should filter air just as well as a paper filter. The dirt helps aid in the filter performance. It fills in those hole and then the filter allows increased air flow over a paper filter (not a noticeable amount unless your artificially aspirated a.k.a SC or TC).
Quote from K&N website: "The dirt particles collected on the surface of a K&N element have little effect on air flow during much of its service life because there are no small holes to clog. Particles are stopped by layers of crisscrossed cotton fibers and held in suspension by the oil. As the filter begins to collect debris, an additional form of filter action begins to take place because air must first pass through the dirt particles trapped on the surface. That means a K&N air filter continues to exhibit high air flow throughout the life of the filter while it is accumulating dirt. At the same time, the air flow for an average paper air filter can decrease dramatically as the paper element gets dirty. So as dirt accumulates, the performance advantages of a K&N air filter can increase!
Tests performed by an independent laboratory commonly known as the Frazier Permeability Test have shown that the Medium used in K&N air filters
flows more than 300% more air than paper air filter medium when compared on a square inch per square inch basis. A Square inch comparison is not directly proportional to the increase you can expect from installing a K&N air filter in replacement of a paper air filter due to the effect of such things as filter size, number and depth of pleats. However, you can be assured a K&N air filter will provide dramatically more air flow which can enhance engine performance."
("http://www.knfilters.com/filter_facts.htm", taken on 10/21/2013)
Now I know most of this is probably blowing smoke but it does make sense so I think it might be partly true with all reusable filters.
This is just my $0.02.