I have to agree with the general package comments - today I visited a new shop nearest to me (still about 20 mins away, but nothing has survived in my podunk, apparently muggle town). I came back with The Biggest Grin for hours! The staff was incredibly welcoming, greeting me warmly without pressure, offering assistance, showing me around. She was familiar with knitty.com (bonus!) and actually had a pair of Fetching on display for me to try on and gave me advice on yarn usage should I decide to try it.
The selection is a big deal to me, and a balanced approach is appealing to me, with some sock, some sport and DK, and some Aran and worsted with a few chunky thrown in for fun.

Something that makes a huge impression on me is samples. This particular shop has samples of most of the yarns they carry knitted up into some sort of display. In addition, newer fibers that some of us haven't tried yet (100% soysilk anyone?) have been knitted up and then washed to showcase that end result.

With a comfy sitting area, good lighting, lots of yarn within squishing reach, and knowledgable friendly staff, this is as close to perfect as it can get without the entire stock being free for the taking :)