It would be a nice feature if somewhere in the panels settings you could specify what the default style would be when adding new panes.
For instance we are creating a website right now that almost all of the panes are use the "System Block" style to match the styling normal system blocks get. This means that each time a pane is added you have to remember to go in to the style for that pane and choose the "System Block" style which is a bit of a pain.
You also cannot choose styles in the IPE which means we cant really use the IPE. Each new pane you would add through it you would then have to go into the panel content and manually change the pane style, which makes the IPE not so useful for adding panes, though it is handy for editing them quickly.