Stock compiz currently uses viewports rather than workspaces by default. As of 0.3.4, compiz now supports workspaces and thus should default to them. The following is copied from:
http://www.advogato.org/person/Burgundavia/diary.html?start=115
The biggest problem: Workspaces
Well, lets start with workspaces vs. viewports. Metacity (and I understand most other major WMs) assume each workspace is a discrete entity. Windows are either on one or another. In the physical world, this would represent multiple physical desks. Compiz works differently. It uses something called a viewport, into one workspace. This is what allows you to have windows overlapping the edge of the cube. Think of this as having one really big desk, but you can only see one part of it at a time.
Before I continue, I should talk briefly about the two major types of users of workspaces in the Linux world. I will use the real world data of my office, which is mostly ex-Windows users. The first group, which includes myself and one of the new hires, use multiple workspaces. For us, each workspace is a single entity, with discrete programs on them. The other group, the majority,, use a single workspace for everything. As far as they are considered, workspaces don't exist. (As an aside, yes, I have told all of them about it. They don't really care).
Now that I have explained this, lets talk about how the change in the way workspaces have been changed affects each group. For the first group, the multiple-workspace people, The change is going to drive us nuts. None of the keyboard commands to move a window to the next workspace worked, as, after all, it really was one giant workspace. Further, applications were never really only one viewport, meaning that maximizing never really works and if an application snuck onto the next viewport over, a user like myself, who expects when you switch viewports the active program in that workspace will be selected, found themselves closing tabs in the application in the last viewport, because it had snuck over 5 or 10 pixels and thus was considered still active in your current viewport.
Metacity will flash an active window on all workspaces when the appropriate hint is raised. Compiz? Not so much.
But what about the user who only uses one workspace? For this user, the current workspace/viewport is the only one that will ever exist. This means applications had better not go anywhere. So if a window sneaks into the next viewport over, as it is far too easy to do, they are likely to never find it.
It should still be possible to configure viewports, as I do know what I'm doing, and hate Metacity's workspace model.