I have exactly the same experience, I have worked with some amazing HR people (as clients) at my previous job and we really made a good product that would have been impossible without their fantastic input. They are humans like everone else, and it's a job like any other.
All I'm saying it doesn't matter what your clients are doing as long as you and your product keeps them excited. Even the most stereotypically boring accountants will get excited about a cool product that will actually help them concentrating on their profession in their valuable time by doing the boring, tedious tasks instead of them. While the HR product we made wasn't directly related to recruiting, it made the lives of HR people a lot easier by automating a lot of tedious "paperwork" in a quite innovative and "fun" way.
Everyone, without exceptions, likes fun, innovative, interesting stuff that makes their lives easier. You just have to hit the right chord.
