If you're a newbie knitter with a wad of cash to blow, this is a great place to pick up some novelty yarn-- you know, the kind with little bobbles and ribbons and sparkles-- for your first scarf. If you've ever knitted a sweater, you'll want to go elsewhere. The way they organize their yarn - by color - is spectacularly un-useful, and each bin will have only two or three balls each of widely differing yarn types. They don't carry many of the basic quality brands, and the one time I asked about a particular type they promised to let me know when it came in and then never got back to me. One of the employees is also quite rude.
I highly recommend Knitting Arts in Saratoga. It's a trek from Menlo Park, but well worth the time.