I would find it handy to have label text displayed at different angles - for example text running upwards at 45deg would be nice for labelling a horizontal set of vertical sliders at the top, running down at 45deg for labelling at the bottom. There are situations (eg mixer interfaces) where vsliders are more "natural" than hsliders, and with standard labels they all overlap and it all gets horribly ugly unless the labels are short and uninformative. Maybe even having vertical text (up or down) within the body of the slider would work, saving precious screen space.