intro to tubes

Could some one give me any sites on introduction to tube audio. I'm looking to find answers concerning: What's so great about tubes? How long do tubes last? Are tubes expensive? Are tubes still manufactured(why do i hear so much about vintage tubes)? How are tube amps differet from solid state? What are the benefits? any help would be great. I just think they look cool. I know that newbies in the hobby get shafted on message boards, but please take the time to answer my questions.