Will they try to compete with storage solutions already in place like STORJ and SIACOIN?
If I am reading their site correctly, do users lend out their hard drive on the SHIFT network so that people can host their websites on another person's hard drive?
AFAIK STORJ and SIACOIN have focused on decentralized storage and not websites, like SHIFT. So there might be some overlaps, but it isn't a direct competitor in this sense.
To answer your other question: People are going to be able to lend out their hard drive (node) on the SHIFT network for other people websites and earn SHIFT.