I've been using mines fairly well for the way I play, which is usually in pugs and very heavy in terrain use and ambush setting.
Essentially I've been using the Mines the same way I use Tar, not always to do damage, but to prevent a ship from going in a direction I don't want them to go so I can get into a better position.
The problem I've had with the Mine launcher is coordinating it soon enough with my Gunners. A good pilot as a gunner would likely know where to put a mine for maximum affect, a great Gunner would likely know as well but a decent gunner isn't as quick with figuring out how to best use an ambush weapon that requires some fore thought.
Though I've had some luck with telling a gunner to just spread a field of mines and I try to work it into the dance of death as we go.
I'm still of the opinion piercing does to much damage to quickly to Armor. I like the utility we have with the different guns and various play styles that can be achieved, but I feel strongly that more diversity could be found, more use for various ammos, if the over-all effectiveness of piercing was brought down so breaking a ships Armor is more a result of overwhelming the teams Engineers with good positioning, timing and applied spread grouped weapons from multiple ships, rather than a single ship with a good dual or trifecta combination that requires piercing as part of its damage equation.