According to the Cornell Lab of Ornithology--" ...Some people include this as suitable bird nesting material. Others recommend against it because it is porous and dries out poorly if it's rained on in the nest. Still others warn that wet dryer lint dries into a hard mass, providing poor nest insulation, however this may happen only if it contains laundry detergent or fabric softener residue. More information is needed before we can recommend offering dryer lint."
In the last 10 years or so I have heard never to use dryer lint and from many different sources. All for the same reasons as stated above. We always put our dogs fur outside for the birds and were always amazed at how fast it would disapear.
The Cornell site has a list of preferred nesting material - www.birds.cornell.edu
under attracting birds.
Isn't this a wonderful time of year?!