There are several factors at play here. Firstly, there is the dominance of the Microsoft operating system and peoples' inherent desire stay with the an operating system that they are familiar with. Secondly, there is a bit of a learning curve. The operating systems are not identical and therefore there are some things that must be relearned. Thirdly, in the corporate world, the short term cost of retraining employees/rehiring IT may seem to exceed the money that would be saved using 'free' operating systems. Another factor is the 'mis'conception that Linux is a command line based operating system. This makes adopting Linux seem daunting.
It's not really more vulnerable. Windows is more widely used so it has more viruses written for it.
Absolutely. Very widely used. Actually, this very site runs on Linux...
No. Universities use Microsoft Windows.
The gtkpod software (See links below) is widely used for using an iPod with a Linux system.
Search Google with "jboss in Linux" for more info: Quote from jboss.org: JBoss, a free J2EE 1.4 certified application server, is the most widely used Open Source application server on the market. Unquote.
Computer professionals that are running a dedicated webserver use dedicated Linux servers. Linux servers are currently the most widely used server operating systems in the world.
BIND is the default package for Domain Name service(DNS) in Linux based systems, one of the widely used DNS servers across the internet.
Linux hositng is cheaper because there is less data. Windows based hosting is more commonplace and widely used.
Need to be more specific in your question.
Yes, Linux can be used on a mainframe.
No, the more widely used web browser for a PC are Internet Explorer and Firefox. Opera is one of the more widely used browsers for mobile devices.
Linux home servers are not as common as other servers. One should note that Linux home servers are more likely to be used as a work station rather than a simple server.