Inspired by the folders introduced in iOS 4 and Android 4.0, Groups would be a simple way to collect several application launchers in one place. Simply drag and drop a launcher on top of another and they combine into a Group. This would save space on the Dash for applications that are, for example, used enough to be favorited, but are really only used together, among various other reasons.
Some hastily sketched mockups may help visualize how Groups could work.
There are a number of possible ways Groups could appear visualy. A few are: a stack of icons (not great), a grid of scaled-down icons (doesn't scale very well), or Android style where the icons are a stack, but going into the screen.
When clicked, a Group could display its contents in a popup, allowing switching to/launching/dragging from there. For very large collections, the popup could be multicolumn so no scrolling is required. When the collection becomes too large to fit on screen a scroll bar would be needed. How a multicolumn popup from the Dash works with the window picker needs some thought since the current goal is to have popups from the Dash push the scaled windows over so that it does not overlap them.
This would look similar to the applications stack on Mac OS X (>10.6).
An alternative option to a popup would be to have the Group actually switch the Dash contents to the Group's contents. A back arrow is placed as the first item in the Dash, which will switch the Dash back to it's original favorites list. This would allow a user to create different contexts that they can switch between. For example, a "Develop" group that contains the applications most used in a development session could be utilized so that when desired, the Dash can show just the relevant applications to the user's current work and their master favorites list remains relatively uncluttered.
An options popup (right click/long press) could present an editable name for the Group, a way to launch all applications in the Group, and any other utility function deemed necessary. This seems like an unnecessary complication though, all the apps could be launched just by dragging the Group to a workspace and the ability to name/rename a Group shouldn't be in some options menu. The name would likely be shown at the top of a popup (in which clicking on it should allow editing) or on top of the Dash if a context switching method is utilized (in this case a popup menu could be useful since getting the name to look right somewhere around the Dash could be hard).