It seems like it is more efficient to look for specific applications, or at least use keywords to search for what you want. When I wanted to find alternative Twitter clients aside from Gwibber, I just searched on "Twitter", and came up with five options. One cool feature is that Ubuntu Software Center displays the rating of the apps as well to help you tell at a glance which ones users like, and which ones are probably duds.
The Ubuntu Software Center is also where you can go to remove apps that are already installed. In the left pane of the display, click on Installed Software. All of the installed apps will display in the right pane. You can select any of them to view more details about the app, or click on Remove to uninstall the app from the system.
I really like the Ubuntu Software Center. But, for those who have put it on a pedestal as the ultimate source of software solutions, I have run into two instances already where it wouldn't really help. First, on Day 9 when I was looking for Twitter tools, my search returned five choices, but Tweetdeck--the best Twitter client in my opinion--wasn't one of them because it is an Adobe Air app that isn't included in the Ubuntu Software Center.
The other situation is related to trying to get hooked up with the PCWorld VPN. I got a few comments offering guidance to just use this app or that app instead of the actual Cisco AnyConnect VPN client. First of all, it never would have occurred to me that I can just use some random open source VPN tool to connect with the PCWorld VPN. If I was to search the Ubuntu Software Center, it would be for "AnyConnect". In fact, I did search that before going to PCWorld tech support and came up empty.
Second, some of the suggestions involve adding or opening additional software repositories. So, even if it occurred to me that a third-party open source VPN app was an option, I would also have to know which repository it can be found in, and add that repository to the Ubuntu Software Center first.
It is nice that it is possible to do those things, and given time and support from helpful Linux community members, users will eventually discover these tricks. But, for someone just jumping into Linux and trying to set up basic tools and connectivity, that is not the most fluid or intuitive solution.