I knit a lot of hats for charity when I don't know what I want to knit yet. It's been great for stash busting. I like knitting toys and baby stuff, but don't have much call for that right now. I'm working on a pillow cover and a sweater right at the moment.
I can't wear hand knit socks so I don't bother and I'm not really a "cozy" person either. I would go mad trying together my phone out of one to answer and it would catch on keys and zippers in my purse. If I did something like stop at Starbucks and take my coffee out for a walk or to work I can see the value of a cup cozy (those cups get hot!), but for my coffee mug at home no.