Ubuntu Software Center, Evolved
In 9.10, the Ubuntu Software Center made its debut, replacing the Add/Remove Applications utility. My biggest complaints with Karmic's software center were the loss of functionality, namely the inability to arrange apps by their popularity star rating, and the extraneous number of mouse clicks needed to download more than one application at a time.
The good news is that, while there are still no check boxes to select multiple applications, you no longer need to go to an application's information page to download it. Apps can be sent to the download/install queue via the Install button, visible immediately from the browse/search results screen. While still not as efficient as Add/Remove Applications, this reduces the number of mouse clicks needed to navigate the Ubuntu Software Center considerably.
The bad news is that the star ratings for popularity (a good way to find the best apps) are still missing, though I believe the ranking of apps on the search results screen does take popularity into account, placing the most popular apps first. This can be seen by doing a quick search for something like “audio,” “video,” or “image.” You'll see that the most notable apps are listed first, not alphabetically or by whether or not the applications are already installed. While this is a definitely a good thing, the ability to sort by popularity without entering any search terms used to be a good way to find quality software.
Fortunately, the Ubuntu Software Center has also received a significant addition in this release: it now also manages any Personal Package Archives (PPAs). A PPA is another way to install software that I haven't yet covered. PPAs come in handy when the distribution you're using doesn't (and won't) have the latest version of an application in its repositories. One of the best examples of needing a PPA is Firefox. Though it's installed by default, the version of Mozilla Firefox included in Ubuntu will not update to major version changes. For example, Ubuntu 9.10 came with Firefox version 3.5.3 installed, and over time, it automatically updated to 3.5.8 through the Ubuntu repositories. However, if you want that 20 percent speed gain from Firefox 3.6, you're out of luck. In order to get the latest Firefox, you need to tell the OS to look somewhere other than the Ubuntu repos. This is where PPAs come in. Think of them as additional mini-repos that usually add access to a single application. So, if you want the latest version of Firefox on a Karmic machine, you would need to add the official Firefox stable PPA which looks like this...
...into your Software Sources via System/Administration/Software Sources. By adding that address, you will now find the latest version of Firefox listed in the package manager. Before version 9.10 Karmic Koala, users had to go through multiple steps to add additional repositories. Karmic simplified the process into a single copy and paste operation. In Lucid, the management of this funcionality is baked right into the Ubuntu Software Center.
Another advantage of this is .deb management. Some newer .deb files not only install an application, but also the corresponding PPA so that that application can receive updates. A good example of this is Google Chrome. The .deb file for Google Chrome automatically adds the official Google Chrome PPA to your system so that there is no need to uninstall it and reinstall when a new version is released. The PPA allows Chrome to update itself. By keeping track of PPAs in the Ubuntu Software Center, it is much easier to see which .debs install a PPA. This also lets the user remove applications added through a PPA or a .deb directly from the Ubuntu Software Center, keeping more software management tasks within a single utility.
After the huge leap backwards that was Karmic's Ubuntu Software Center, the Lucid Ubuntu Software Center has made a handful of baby steps in what we'd consider the right direction. The ultimate goal of the Ubuntu Software Center is to replace multiple separate application management utilities: Add/Remove Applications, Computer Janitor, Software Sources, Synaptic Package Manager, and Update Manager. In 9.10, Add/Remove Applications was the only utility to get replaced (and poorly, we might add). The Ubuntu Software Center in Lucid doesn't quite expand the scope of the app. It does feel like a change from Add/Remove Applications, and not a regression.