I served as a juror in a murder trial in Superior Court in the SF Bay Area a few years ago. I took copious notes during the trial, as did several other jurors. There was no objection by the Court to this note-taking. During the deliberations I (and other jurors) referred to these notes.
I see nothing wrong with the practice of note-taking by jurors. Of course, these notes are for the juror’s use and jury deliberations only. I think that the notes should be subject to certain rules regarding confidential and privileged information. I made a point of burning my 14 pages of handwritten notes after we reached our verdict.