I'd like to say that this is the best forum for pool owners on the entire net. I have come back to this forum to help figure out and solve pool issues, and I have always found the answer here!
I have had the same problem with pinholes this summer, with my 3-year-old above ground pool. I thought it was moles burrowing around the edges of the pool (which has happened), and gnawing on the liner from underneath. I patched about 15 pinholes in June, spread mole repellent around the perimeter of the pool, and thought I had the problem solved. Until yesterday.
Last week, I closed and covered the pool. I noticed on Friday that the water level under the cover seemed low, and by Saturday morning, I could see it was VERY low. I checked the water level through the skimmer, and could feel that the water level was even below the level of the return hole! With a sinking feeling, I started looking for evidence of leaks around the outside perimeter of the pool, and soon found an area of squishy, very fluid mud. With a sigh and a curse, I gathered the troops and took off the cover, got into the very cold, waist-deep pool, and started looking for pinholes. Found about 12, all in the area of the leak I found on the outside. I gathered the patching kit and goggles, and started patching all the pinholes. It, in short, sucked in that cold water.
I started refilling last night, and I'm keeping my fingers crossed that there won't be more pinholes in January. Reading this thread, I'm considering pulling the liner, putting down insecticide, and refilling now, like Jeff74. As much as I don't want to do that, I definitely don't want to have to deal with leaks and patching during the winter. :x