Always, always, always.
Put yourself in the client's chair. Wouldn't you like to know that your tech was doing everything she/he could to ensure you are getting appropriate treatment and that you are cared about as a whole not just someone paying for a nail treatment (or whatever)?
I too take note of birthdays so we can be sure to send a card at the right time, but also email addresses and mobile phone numbers and permission to use for promotions. See this as an opportunity to build a solid database for marketing, look back on the card, she bought cuticle oil in February - she must have run out by now, upsell your products, what about trying this lovely new hand cream too. Next time she's in, you remember you sold her the hand cream how does she like it, you know we do a heel balm in the same range, how about using this for a week and coming in for a nice pedicure next week? Upsell your services.
Make a note of occupation so you can make informed choices about the treatment you are offering. A lady who teaches piano isn't going to want long nails but she'll want them to be strong. Someone in PR will want her nails to always look perfect. Upsell matching toes. Note that she likes red - when a new red comes out you can suggest to her she may like to try one of the new reds.
Make notes about silly things, takes white tea with one sugar, the cat went to the vets last time - how is the cat? It shows the customer you care about them and their custom, and when a cheaper tech starts trading up the road, the client will be less likely to switch as there will be a loyalty to your service.
I could go on - having been in customer service, this touchy feely stuff is my passion. However, on a serious note, sadly we are in a very litigious society. I hate the expression but cover your back. Your insurer won't take kindly to a claim if you haven't documented any relevant notes - it could backfire on you and then you lose big style. It only takes a short while to fill in the consult...
