the short answer is too much!
At a hospital where I used to work we had 'hover matts' however not sure they are still used. They were great for lifting in that they created a cushion of air enabling three people (one for tube and two for lift) to move just about any size patient with ease. that is up the bed, out of the bed and from bed to CT table. there is always a but though and the bigs buts were pressure areas (the addition of the mat beneath the patient cancelled out the low air loss mattress) and infection control.
http://www.hovermatt.com/
from the land down under
Nursing News