4. Make sure all your media files play
Start double-clicking your various audio and video files to see if they play. (You'll find links to your Home folder and your Windows partition -- if you have one -- in the Places menu, so start there to find your media collection.) When Feisty encounters a file type it doesn't know how to handle, an automated codec installer will pop up to try to help you download and install support for the file in question.
If you find video files in your collection that do not play properly no matter what you try, use Automatix (see above) to install the AUD-DVD Codecs collection of packages; then use Synaptic (see below) to install the Totem-xine package, and try your videos again. (This procedure disables Feisty's ability to automatically search for codecs, but you're taking this step only if that functionality fails you in the first place.)
5. Give Desktop Effects a shot
If you have a decent graphics card with 3D capabilities, it's totally worth your while to see if Desktop Effects (an experimental feature set that brings gee-whiz 3D effects to the Linux desktop) will run well on your system. (The features work reliably on some machines, crash after a while on others, and completely garble the display on particularly unlucky PCs -- hence the designation "experimental.")
To try out Desktop Effects, select System, Preferences, Desktop Effects. When the 'Enable the driver?' dialog box pops up, click Enable Driver. You'll now be prompted to restart your computer (a rare thing in Linux land).
Once you do, log back in and select System, Preferences, Desktop Effects again. In the new dialog box, click the Enable Desktop Effects button. After a few moments of on-screen craziness, your desktop should reappear, looking as it did before. But you'll notice a difference the moment you drag a window or open a drop-down menu. (Yowza, look at that!)
If everything looks good, click Keep Settings in the dialog box asking you to confirm the change. (If things look bad, this is your first chance to bail out. If things are so poor you can't even see the dialog box, have no fear: Feisty will automatically revert to your former settings after 30 seconds.)
Try enabling the workspace-switching effect back in the Desktop Effects box; when you click to a different workspace (via the widget in the lower right of your screen), you should see a nifty effect. Also note the altered behavior when you press Alt-Tab.
If you don't like what you see with Desktop Effects (or if you find that your system becomes crash-prone or otherwise behaves oddly with the Effects, uh, in effect), you can turn them off by once again summoning the Desktop Effects dialog box and clicking Enable Desktop Effects. Yes, you read that right: The button behaves as a toggle -- though, alas, at this point in time its label doesn't change to 'Disable Desktop Effects' to indicate this to the user. But clicking the button when effects are enabled disables them, as you will see if you click the button and then move a window around.