Ubuntu doesn't have a built-in settings GUI to disable Unity lenses and the only way to remove a lens from Dash is to uninstall it. If you only want to temporarily disable some Unity lenses, you can use an application called Lens Toggle.
Lens Toggle comes with a very simple user interface from which you can select to enable or disable some or all installed Unity lenses, including the default Applications, Files, Music and Video lenses. The application may be simple, but it's very useful now that there are so many Unity lenses available.
To install Lens Toggle in Ubuntu 12.04 Precise Pangolin, use the following commands:
Once installed, launch LensToggle from Dash.
sudo add-apt-repository ppa:aking1012-com/lenstoggle sudo apt-get update sudo apt-get install python-lenstoggler
After you've made some changes, click the Apply button in Lens Toggle and restart Unity (by typing "setsid unity" in a terminal) or log out and log back in. That's required because the application doesn't restart Unity automatically.