In a bug report in launchapd , Mark Shuttleworth has commented that all the icons on Unity launcher will be movable in Ubuntu 11.10 Oneiric Ocelot except trash which will always remain at the bottom.
Not being able to move lenses and worksapce switcher icons on Unity launcher at any desired place is one of the most annoying problems in Natty. The problem will be most probably fixed in 11.10
Here is what he said:
I think we'd like to move to having much more flexibility, with the exception of Trash always being at the bottom. So you should be able to move or remove Apps, Files and Workspaces.
Just to be clear, in Oneiric it should be possible to add or remove any Place AND the Workspace switcher to the Launcher. The experience for each of these should be: you search through the Dash, find them, drag them to the launcher and can put them wherever you want. The only fixed-location item in the Launcher will be Trash.
[via Ubuntu Secrets]