How common is bacterial mediated transformation? In plants? In animal cells?
In animal cells the process is called transfection, to differentiate from transformation which is the process by which cells become immortalized (cancerous). I'm mainly familiar with mammalian cells, and in these systems some reaction is required to open pores of some sort in the cell membrane to allow the genetic material to enter. Viruses can mediate cellular entry on their own, but I am unaware of any method that uses live bacteria (although this doesn't mean that some specialized method doesn't exist).