I noticed my garden has bare patches too, so I'm going to fork mine over and sprinkle some grass seed down & see what happens, I used weed and feed last year so it may be where a weed may of been, Lawns do need looking after. Also if you have a dog it could kill off grass patches.

Apparently a lot of lawns have suffered where there was a lot of snow over the Winter. Where the air was trapped between the ground and the snow the grass died so it could be a hang over from the winter.