(If there's a better place for enhancement requests, please tell me where.)
Currently the only way to change a chart's value (Y) series titles from their defaults of "Series<n>" is to manually enter text in the Format Chart tab's Series area. I'd like to be able to specify those titles via the report's dataset; an obvious option would be the name of the column from which the series data is taken - and another nice option would be to specify a row within that column.