There are also disadvantages to using an oiled cotton filter element.
1. They don't filter as well as a dry paper element until they collect a little dirt ... even then, they allow more fine particles into your engine than paper.
2. They must be cleaned gently before reuse, or you can damage the filter material.
3. When re-oiling the filter, adding too little oil compromises filtration. Adding too much oil can damage your MAF sensor.
4. They're noisier than the stock system.
Although it's a fact that wet filters allow greater airflow, there's some debate about how much air a non-turbo, non-s/c engine needs, as well as the location in the powerband where the advantage occurs compared to where the power is needed.
Here's a technical report comparing wet and dry air filters
http://home.usadatanet.net/~jbplock/ISO5011/SPICER.htm
Here's a link to a high-flow dry filter system that I'm researching. Supposedly it has all the advantages of the oiled filter and fewer of the disadvantages.
http://trucks.aempower.com/