Although I do machine quilt for charities and when a gift is in need of finishing, I really do prefer handwork.
The same as all the reasons mentioned above, it's relaxing, it's portable and I think it's a more sociable way of making a quilt.
I can sit with the family and sew or pin, early morning bus rides to work don't seem so brain-draining as I can sew, so long as it's already pinned. I put each block into a separate little freezer bag so that I haven't got several pieces to sort out whilst travelling.
As others, I am definitely more accurate with hand sewing than on the machine.
And, I've got to be honest here and admit it... it feels damn good to look at your finished, handsewn quilt after all those months of work... and tell it how lovely it is, how well it behaved whilst you were making it, then pat it and tell it how well loved it is... lol!
(Sorry, been sewing most of today... I think my brains gone a bit addled!)