The main focus of second grade math is generally adding and subtracting two (and possibly three) digit numbers with regrouping. There is also some multiplication--generally up to the fives, some work with simple fractions, money calculations, and calculations with other units (inches to feet, for example). I would not say it's just marking time. I felt that second grade was where things finally picked up for a bit.
(I'm basing this on experience as a homeschooler with both the Saxon and Singapore math programs. I know that reform math programs in schools--like Investigations and Everyday Math--are different.)
