I run trails quite often and just use regular trainers and never have a problem.
I for sure never run in muddy conditions and muddy conditions don't occur very often where I live.
What are other's thoughts on trail running shoes which provide increased levels of traction. Do you feel it is necessary? How so? If there are ever times where I slip around a bit it's on large rocks with loose gravel on top. Not sure trail shoes with their extra lugs on the bottom would help in that specific scenario, but maybe I'm totally wrong.