As someone else mentioned, this site has become known and is very popular among Korean co-teachers now. This is undoubtedly what caused the huge surge. It really doesn't surprise me as most Korean co-teachers I know love to copy other people's ideas/activities instead of thinking of/making their own. Having been here for a few years now, I notice that whenever I revisit a lesson with a different co-teacher they use the EXACT SAME PPT slides and activities as the previous teacher. There are several Korean sites which KET use religiously for lessons with adaptation.
I personally find it frustrating that many KET take pre-fabricated lessons and teach them exactly as found. This bothers me because: 1)I'm an certified teacher back in my home country and we learn that personalizing/modifying lessons to our interests, passions, strengths as teachers but more importantly to the needs and interests of our students is extremely important. 2) KET's learn these exact same educational theories and philosophy but ignore them. 3) The students get really bored of doing the few same activities, learning strategies OVER and OVER and OVER again.
As a professional teacher, collegiality and sharing of resources really helps to improve the quality of lessons and education. It's also a tremendous help to new teachers. However, copying resources without contributing new ones and using them without modifications to accommodate the teacher's teaching style and the needs of the students only waters down the resources, lessons and education. I maintain my own site of lesson plans and share it with fellow NET's in my region because I know and trust them to adapt my materials and lesson plans to their classes while reciprocally sharing their ideas with me. I use to share my site with the extra class (cheryeong class - sorry no korean keyboard) KET's until I realized they were taking my exact lessons and resources and teaching it to my students before my scheduled class so the students had already completed the activities, played the games, knew the answers/tricks and were bored because they didn't want to repeat the same lesson twice in a row.
It's probably too late but I'd like to suggest that rather than charging a fee for all members, restrict membership access to NET's by way of Alien Registration Card number. The ARC number is composed of 13 digits with the first 8 digits indicating birthday and the 9th digit indicating sex and origin.
For the 9th digit it's as follows: 5 (foreign male 1900-1999), 6 (foreign female 1900-1999), 7 (foreign male 2000-2099), 8 (foreign female 2000-2099).
In addition, I think the idea of having a minimum of 5 posted resources in order to download freely is a great idea. But for brand new NET teachers with little to no training this task could seem daunting. Perhaps a trial or grace period could be allowed...ex: 5 free downloads or 1 month trial, then 5 resources must be uploaded by that member before they can access further/unlimited downloads.
I'm suggesting this for the above reasons, because KET's already have access to several very large and extensive lesson planning sites, while this is really the only site of comparison for NET's (good job waygook!) This would help to ensure that NET's have one exceptional resource with untapped/fresh ideas. I'd also like to add that one of the main reasons NET's are hired and placed in Korean schools is for our fresh ideas, activities and our ability to teach the culture. If these are all packaged up in nice tidy PPTs, worksheets, activities, games and made accessible to KET's, not only may they be used out of context or incorrectly, but NET jobs here become redundant...might as well upload this site onto the new teaching robots

For any KET's reading this: I do not think ALL KET's teachers copy & paste materials without contributing and ignore the need to adapt/modify lessons for their students. I have met a few, though rare, KET's who make original creative lessons, use a variety of activities and learning strategies to engage student interest and help them improve, adapt my resources well, and share ideas of their own. Unfortunately, the majority of KET's I've met, known, taught with, heard about have ruined it for the few which really strive to make a difference in English education in Korea.