What is the difference between ToolStripSplitButton and ToolStripDropDownButton? (Visual Studio 2008) (Also asked here, not on SO). At first blush, they seem to be largly the same; especially in the designer.
Split buttons are regular buttons with a drop-down menu attached to them. If you click a split button on the button part, it acts like a regular button. If you click it on the menu part, a menu drops down. The "back" button on the majority of browsers are this type of button, for example.
Drop-down buttons, when clicked, drop down a menu. They don't have (and shouldn't have) directly associated functionality beyond displaying the drop-down menu. They are like the topmost items in a menu: they don't do anything when clicked other than to show you more items.