Though I'm not there this year (some of my colleagues will be), San Diego rates as one of my favourite ACS national meeting venues. I'll let you into a secret: attending ACS meetings is about far more than attending talks and poster sessions. Thus, the location of the convention centre and its proximity to entertainment (pick your vice) is pretty important. The convention center itself is on Harbor drive, and all you need do is cross the tram tracks and you're in the gaslamp quarter "a walkable urban playground" with plenty of restaurants, bars, theatres to entertain you.
I can recommend the Altitude Sky Lounge - a 22nd floor rooftop bar - with some awesome views (including right down into Petco park (San Diego Padres' stadium). Also I recall a particular evening where many (in)famous chemists were customers at the Cuban cigar factory (remember smoking tobacco is bad for you and this should in no way be taken as encouragement).
Right that's it for recommendations for now. Why not share your own? That way I'll know what to look out for next time the chemistry circus hits San Diego. Oh, you can tell us about some of the cool talks you've seen too, if you must ;-)