Ubuntu is one of countless Linux flavours. Users have plenty of choice when it comes to Linux, yet Ubuntu has become a clear winner. Why? There are many reasons, I'm sure each of you will have a different reason but for me apt-get is the killer app.
I first looked at Linux when Red Hat was King; I purchased Red Hat 5.1 in fact I still have the boxed set on a bookshelf somewhere. Things have changed since then; when I think back my biggest complaint and I think many novice users would agree was the hassle of installing software. Downloading and compiling from source was a sad state of affairs. On the other hand once you got comfortable with ./configure ./make and all that jazz you have dependancy hell to deal with. No wonder many were turned off by Linux. Some of you may argue rpm's helped, yes I would agree. But if there was a dependancy problem rpm's were rather useless. I recall countless hours of shear agony and frustation attempting dependancy resolution.
Enter Debian based Ubuntu with apt-get and its repository heaven.