Hi Marianne! Sorry for the late response.
My experience with the J. Crew personal shopper has been really great. Each store has one personal shopper per store (I'm not sure but larger stores might have two), and they are hired for that specific position. I'm sure the shoppers vary depending on personality, but the PS at my J. Crew is wonderful. She's very honest and does help me with choosing colors and accessorizing things. Because I have worked with her whenever I've shopped (which has been often), she is familiar with my lifestyle and my personal style, so her suggestions are always good (she even remembers things I've bought in the past so can suggest new items to work into my existing wardrobe). She is also very honest and good with fit, too.
Another nice thing about my personal shopper is that she always notifies me about special store events, when the store is having a major sale, and also she lets me know when the store gets an item that I have seen somewhere and asked about (online or in a magazine), so I can come see it in person.
These are all things that have built over time because I've worked with her a lot. My advice would to definitely try it out. Because most of the benefits come from working the personal shopper over time, I'd just see if you like her and your personalities meld. Be really honest about what your lifestyle is like, the type of clothing you generally wear, your clothing needs, etc, so she can start to build a profile for you and make suggestions that are helpful in building your wardrobe. She'll probably also show you some things that might be out of your box a little. It's up to you whether you want to try it or not. I always try everything, because sometimes I am pleasantly surprised (my personal shopper Lauren was the one who suggested I get the yellow flower belt when it went on sale and it's one of my favorite accessories now).
If worse comes to worse and for some reason you don't enjoy your experience, you at least get a discount for your troubles, which is great (J. Crew has a lot of nice things in right now). But I definitely say give it a try.
Hope this helps a little! Let me know if you have any other questions.