I think of two positions at Nordstrom ~ there's the sales associate and there's the personal shopper. As has been mentioned before, any SA can operate as a personal shopper. One of the things I love about Nordies is that stellar service that's clearly encoded in the way the store is run. SAs are not limited to working in their assigned department; they can, and often do, look for items for customers throughout the store.
When I started going to Nordstrom, SAs always came up to ask if I needed help ~ always done in a nice, un-pushy way, I might add. I usually had a question or two for them, an item I was looking for, etc. At the end I always asked for their card if I liked the service. Pretty quickly I felt that I had a decent grasp of who was really helpful and someone I could click with. Unfortunately my store is a training store so staff rotate out a lot. You can always ask for or look for the person who heads a certain department as another way to find someone who might be good to work with. I have worked with quite a few people and have never felt an obligation to stick with just one person if that person wasn't working out for me. But then, I haven't had lots of people calling me regularly as follow-up (I wish some of them would have).
I have also requested appointments with personal shoppers. Two did not work out for me but I believe the latest one will be the one I can build a great relationship with. There is a person in charge of customer relations at each store that can help match you to a personal shopper if you want.
My current personal shopper is sending me emails about sales; she also told me to put a list together of holes in my wardrobe I'd like to fill during NAS. In general I've relied on SAs to help me determine the right fit for jeans ~ I am really bad at figuring that out, especially since some brands stretch out more than others. An SA I worked with in the shoe department will call me if something comes in she knows I am looking for. I've had lots of SAs and the shopper help me track down my size when it wasn't in the store. Stuff like that.