I can travel to SF for a conference either mid October,2006 or late July/early August 2007. Either trip would be four or five days. Which time of year is preferable?

I'd choose October. You wont have the summer crowds and you are likely to have better weather. In October, the summer fog is generally gone and the winter rains haven't started yet. July and August can be chilly - hot temperatures inland cause a coastal inversion layer which draws in the fog. It can sometimes be quite heavy. Some fog is part of the SF experience, but it is hard to appreciate the golden gate bridge when you can't see it

Ditto what J Correa said-October is MUCH
better weatherwise and crowd-wise

R5

October 2006. Why put it off?
And seconding the other posters re the weather, although the weather pattern is harder to predict these days. Mid-October is nice in San Francisco, with the awareness that each warm day might be the last of the season - it's that melancholy autumn thing, although with us it's our poignant Indian Summer thing.

Oct?
July/Aug??:-?

"Yes"!

Ditto. ITA, Mid October is great for both the less crowds and really nice weather.

Ok everyone, it's a no brainer for October! Thanks for your input!