I have stayed at this hotel on three occasions for work. My first two stays were sublime. I had large, clean, and classic Westin comfortable rooms. The staff was attentive, polite and efficient (though the reception queue is always too long).
However, on my third stay I was put up in the old wing. I did not realize there was even an old wing until this stay. The room was half the size, oddly shaped, and the walls were paper thin. I could hear everything that went on outside my room. And as luck would not have it, two men had a long and loud conversation at 4 am, shattering my sleep and exacerbating my jet lag.
Either way, the location is fantastic for the San Fran business visit as is it is close to a lot of the offices around Union Square and a five minute drive to the main freeway for access to the whole Bay/Valley area.
So, love the place in the new wing, hate the place in the old wing and with so much competition nearby and not prepared to take the risk again.