I travelled into the US [SFO] at the end of November last year and re-entered in the middle of December [SFO] ... no problems encountered at all.

On my second visit, the immigration officer asked me when was the last time I was in the US .. I gave him the exact date in November. He asked me how long will I be staying this time and I answered truthfully ie 3 days. No further questions and he stamped my passport.