Sophie's Yarns recently relocated from Antique Row to Fabric Row (4th and Bainbridge), and their new shop is spacious and bright. The two regular staff members, Rachel and Ubaldo are absolute knitting gurus, and if you ever need help with anything you're knitting or even thinking of knitting, they are an excellent resource.
The store's best asset, in my opinion, has always been the cats. Two cats call the store their own, and they can often be found lounging on a table or a window sill, and most of the time (like all cats), they love a bit of attention. So if you're allergic to cats, keep that in mind.
My major issue with the store is the yarn selection. There is never, ever a constant brand or type of yarn available--it changes constantly. This would be great if you liked a lot of variety, but the fact that I can't expect to find something there all the time (a staple, if you will) really bothers me. They offer a huge assortment of novelty yarns and luxury yarns, and there's always a decent stock of baby yarns, but there's never really much else. They've recently moved, so their selection is a bit slim, but their stock has always been a bit on the small side.
This is definitely the place to go if you need some assistance, and I recommend their classes, but don't expect to find yarn or patterns or notions that you'll definitely want most of the time.