Linux (Any Distribution or "Distro") is a very complex operating system that should only be used by persons that have an advanced understanding of computers. While Linux is widely used for, and somewhat intended, for use on servers, OS's like Ubuntu, Gnome, Debian, etc. are usually optimized for use on a Personal Home Computer.
Linux takes up A lot less space than Any of the Windows Operating Systems, leaving somewhere in the Range of 280 to even 300GB of Space left on a 320GB Hard Drive. As far as Random Access Memory (RAM) goes, Linux uses nowhere near as much memory as Windows. All of it's applications and programs are built to consume less memory, while at the same time running at speeds meeting or surpassing Windows application start-ups and use.
Viruses are a very Rare occurrence on Linux Operating Systems. Like a McIntosh Linux Distributions are written with a different Shell than that of Windows. Windows is (Obviously) the most widely used and popular Operating System, that has a Shell know as "Batch", Or .BAT. Over the years, hackers have found ways to exploit this shell and target it with damaging viruses. In this case, Macintosh and Linux Operating Systems get viruses less often because they are not as widely used as Windows; Most Hackers seeing it as a waste of time to build a virus that targets less used Operating Systems like Linux. It is believed that Linux is the most unlikely to get a virus of the three.
In the case, of programs you are somewhat limited. Most software (and Hardware) is not optimized for use with Linux. To Run games and a majority of Third-Party Software, examples being Adobe Photoshop, one would have to run it through a program known as WINE. Do note that some Linux Distros are not capable of Running this Software. When Linux is installed, you have a selection of Software that is preinstalled that should meet most needs. An Office Suite and Photo viewer among the many others, but this can vary on the Linux Distribution chosen.
Installing Programs can pose a bit of a challenge in Linux. Linux is not able to Run any .exe files (WINE only is compatible with a select type) making Installing a tricky task. In most cases you will have to extract the files, TAR.GZ, .DEB, and .RPM among the most popular, and use the "Terminal", A Command Prompt like Hub that is the control center of the OS, to install it MANUALLY.
An Example of an "Install Code" is this. Apt/get install WineHQ.tar.gz. You will have to do this almost every time you want to install a program, unless you have an application that automatically installs the program. RPM files are mainly auto installed though, but they are mostly configured for the GNOME Distribution.
Linux is truly an Operating System in which you do everything yourself. But at that cost, Linux is compatible with a very limited amount of programs, and is sometimes even incompatible with SOME Peripheral Devices (Mice, Keyboards, Printers, etc.). So there is a good chance that you will lose the ability to run and use may of your favorite programs. But, there are some upsides. It is almost unheard of Linux crashing (BSODs are non-existent) and the ability for a Linux Machine to run for literally months on end without the need for a shut-down.
I personally would not recommend you download and using Ubuntu Linux as your Default Operating System. If you still think that you would like the opportunity to learn more about the Operating System, Manual operation, and even the Computer as a whole, you can download it as a Live-CD demo which offers all of the features and programs of Ubuntu without the Operating System actually Reformatting your Hard Drive.
If you do wish to put Ubuntu Linux as your default OS, be warned that (No Offense) inexperienced users such as yourself are entering into dangerous territory. But, Linux gives you the opportunity to learn things new that you never knew before about a computer. Linux is always changing and evolving, leaving the users to adapt to the change and make the system Their's Truly.
Play! Experiment with the Operating System using the Live-CD demo (Just be sure that you do not activate the install through the disk) and get to know it. Get a Feel for the new User Interface, and look at it opposed to Windows. You may like it and decide to select it as your primary OS, that is a good thing! Believe it or not, many Technology companies would be impressed to learn that you have had experience with an Operating System that is So user Reliant!
Just be sure that you have gotten a feel for the OS as a whole, that you are prepared to work with the OS, and that just in case you want to go back to Windows that you have everything backed up onto an external Hard Drive.
You do what you think is Best based on this information!