1. Copying Layer Styles
Say you have a text layer with a drop shadow, bevel, outer glow etc
etc and you want to apply that style to another layer. You can simply
go to the layer that has that layer style applied to it, control
click (mac) or right click (pc) on the layer style icon in that layer
and choose "Copy Layer Style" from the pop-up menu that appears. You
can then choose a layer that you want to apply that layer style to
and control or right click on that, and choose "Paste Layer Style"
from the pop-up menu to apply that layer style.

2. Breaking Apart Layer Styles
Perhaps you have a layer style applied but its not quite the way you
want it to appear. Perhaps you want to apply a filter to the drop
shadow...well did you know you can break that layer style into
separate layers by control or right clicking on the layer style icon
in that layer and choosing "Create Layers" from the pop-up menu. You
can then target individual layers and apply filters, delete rearrange
etc to your heart's content!

Life is too much fun!