Difference between Adobe Media Encoder CS4, CS5 and CS5.5

Question

What is the main difference between Adobe Media Encoder CS4, CS5 and CS5.5?

- Do they encode differently? 
- Is Adobe Media Encoder CS5.5 better than its predecessor (CS4 and CS5)? 
- Do they have distinct hardware requirements?

Answer 1

Extract from blogs.adobe.com - provided by bZezzz

• Added encoding presets for iPad devices and other tablet devices.
• Improved encoding presets for YouTube, Vimeo, and other popular output formats.
• You can now import image sequences into Adobe Media Encoder.
• Watch folder features are much improved, including ability to add the same watch folder to the encoding queue multiple times and assign multiple sets of encoding settings for multiple output types from the same source. Adding a watch folder is now as easy as dragging a folder into the Watch Folders pane.
• The Start Queue Automatically When Idle For preference is off by default. (Yay!)
• A new checkbox, Auto-Encode Watch Folders, gives you the ability to decide whether items in a watch folder are automatically encoded as soon as they appear, as opposed to waiting until the encoding queue is started.
• Added context menus to many items, so that common commands are available by right-clicking (Windows) or Control-clicking (Mac OS) many items. An especially handy pair of such menu items are Reveal Source File and Reveal Output File, which show the location of the respective file in the Finder or Windows Explorer.
• Added ability to drag a sequence from the Adobe Premiere Pro Project panel or a composition from the After Effects Project panel into Adobe Media Encoder to add it to the encoding queue. You can also begin the process of importing by double-clicking in an empty area of the encoding queue pane.
• RED (R3D) source settings can be accessed using File > Source Settings, with improved RED support like that in After Effects CS5.5 and Adobe Premiere Pro CS5.5, including new color science support (REDcolor2, REDgamma2, REDlogFilm, etc.) and better curves and levels UI.
• A chime sounds when the encoding queue is done processing, like in After Effects.
• The trial versions of Adobe Premiere Pro CS5.5 and After Effects CS5.5 include all codecs included with the full versions, so users of the trial version will be able to import any file that can be imported using in the full version, as well as being able to encode using any codec that can be used in the full version. Because Adobe Media Encoder receives its codecs from the client applications, this change expands the functionality of the Adobe Media Encoder CS5.5 trial version, too.