Rails hosting is like PHP. Your web host needs to have it.
Its (in my opinion) a next generation hyped up language. It is basically a very heavily formatted PHP. There have been a lot of PHP frameworks popping up that emulate rails.
Rails is a MVC based framework, which is what really seperates it. Once you learn it, it takes a lot of the repetative coding out of an application so you can rapidly develop new sites. But then, any framework you learn will let you do that.
Its just another framework/language. Some people think its the greatest thing since canned beer, others could take it or leave it (myself included). Not due to any disadvantages in using it, but I just don't feel like taking the time to learn it.