I'd agree that someone who's looking for a gloriously warm getaway will be disappointed with SF right now (and pretty much all year except for the odd week in sep-oct as already mentioned), but I wouldn't think it would be so cold as to interfere with a visit... I'd pretty much bank on something around 60 during the day, and cool enough at night that you'll be uncomfortable without a coat. It's not Vegas in the summer, but neither is it Wisconsin in the winter And the crowds are reasonably small right now. You may experience a bit of rain, or you may not.

It really is relative... my family is currently visiting from Toronto and they are very happy with the weather. That said... I'm sure that if weather was everything, they'd be even happier about 300 miles farther south