Some people come to linux because they'd like to feel what Mac OS X taste like.
Some can't afford to buy an os x or they just want to check it before they are buying, others do it from ideological reasons such as adherence to freedom and open source.
Whatever the reason may be, they all have one thing in common: making their linux similar to mac OS as possible. You can see evidence for this phenomenon in some distros that aspire to look and feel just like mac such as: Pear OS.
How similar does Linux and Mac really are?
The results are surprising, to understand why is that so, let's start up with some facts: below is a chart showing the 'Evolution of Unix and Unix-like systems'.
As you can see there is no line that connects between Linux and Unix at all, whilst on the other hand OS X (right to linux) does connect to Unix through BSD.
It turns out that Linux unlike Mac does not incorporates Unix in its code base: " a federal district court judge ... ruled on summary judgment that Novell... is the rightful owner of the copyrights covering the Unix operating system... Novell announced... 'We don't believe there is Unix in Linux'. "
So if there's no Unix in Linux, then what makes Linux a Unix-like system?