APC published a very good article that compares Ubuntu to Windows when executing various tasks (mp3 encoding, Web browsing, Media playback, etc). Ubuntu is very good for most of the task sbut remains behing windows for some of them like mp3 encoding and Webcam management. The complete Ubuntu rating is list below:

• First impressions: Pass — No problems. The task can be completed exactly as under Windows.
• Getting Updates: Optimal — Passes with flying colours. The task could not only be completed, but better or easier than under Windows.
• Web browsing: Pass
• Media playback: Iffy — When a task could only be partially completed, or completed but not without issue.
• File management: Pass
• Network shares: Pass
• Uploading to sites: Optimal 
• CD and DVD burning: Optimal 
• MP3 Encoding: Iffy 
• Talking to the iPod: Optimal 
• Taking the upgrade plunge: Optimal 
• Evolutionary email: Optimal 
• Open Office: Optimal 
• Web StarCam: Iffy 
• Plug in Cameras: Flop — Not possible to complete at all. Probably not a good thing.
• USB drives: Optimal 
• Image management: Optimal 
• Image editing: Optimal 
• Printing: Pass 
• Managing disk space: Flop 
• Video production: Optimal 
• Native games: Flop Pass
• Transgaming: Iffy 
• Free games: Optimal