Another new feature for datasheets in the Totals Row. At the bottom of any datasheet view, one can opt to show a row that will do a number of canned aggregation formulas applied to each column, independently. You can see it in action here, where the # of items is shown as "8".
Depending on the type of the column, different aggregations are allowed. For text fields, only a count of the fields in that column that are not empty can be shown. For numeric columns, one can do counts, sum, average, maximum, mininum, standard deviation and variance.
An interesting aspect is that the totals row is pinned to the bottom of the datasheet view (right above the Record Navigator), so you will be able to see it regardless of what data is being shown. There is no need to scroll up and down to see what the aggregation is showing.