I used various methods of FGMO for about 5 years starting with the inverted bottle with pipe cleaner in the entrance and ending with fogging. I had previously detailed my experiences here, but they were discarded when the forums were cleaned. I finally gave up after loosing too many hives this past winter to varroa, and have switched to oxalic acid.
Here is a link that talks some about my experience.http://robo.hydroville.com/html/modules.php?name=News&file=article&sid=8
So far I am very pleased with oxalic acid, after spring treating my few infested hives that made it through the winter, as of last night I still have not seen a mite. Though typically here in the northeast, heavy infestation doesn't happen until the fall. I guess time will tell.