How often should you do user research?
I've found that if you are designing something really important, you should meet with users once a week.
And, what project isn't really important?
How can you meet with users once a week and still have time for design?
I like to build up a "beta design group" of customers that I can call on. I schedule two for every Thursday afternoon.
When I meet with these customers, I watch them use the latest prototype or coded piece of the product that we have at the time.
I try not to slow down the design when preparing for the research study, which can sometimes happen in more rigid design environments where research and design are separate groups.
In my most empowered role, I do both research and design. And, it works well because I can directly adjust the designs on Friday morning and keep on adding to the design until the following Thursday morning (when I prepare to meet with the next set of customers).