At Stigg and Tanitha say, it is very time consuming if you get caught up in it. I had not idea I'd become so addicted, but not spend most of my waking moments playing Wow ... well, when I'm not working at least.
The trial CD should be plentiful and cheap, especially with the Burning Crusade now out. What better time to pull people in to the game than with a new expansion for people to also buy? Give it a shot, see if you like the game, the graphics, the mechanics and storylines. It'll only give you a taste, of course, but it should be good to give you an idea of how much you like the game.
I'm very much a 'casual' player, in that I don't see myself raiding much, beyond adding on to raids looking to fill out their numbers. So even if you do skip the raid content, there is just so much content to experience, and I made it to 60 just this past weekend, and I certainly missed or abandoned a lot of quests along the way. Even with just an hour to play, you can get lots of things done. There are tons of quests where you just deliver goods around, or hunt down mobs in the area, or you could even just go out looking for experience and cash, or work on your professions for fun and profit!

I would reserve instances for when you have your 2-3 hours of time, as you'll probably take this long for a level equivalent instance.
If you do join up, I would recommend finding others to play with. Make friends! Having someone to talk to, quest with and experience the game with is amazing! Having done it myself, I could never see myself soloing a character up all the way. Just know that as with the outside world, there are good people as well as bad people ... but that being said, I think it's just the stories and the odd personal experience that makes it seem like every 9 out of 10 people are jerks. You always remember the bad ones, but not the tons of nice people. It's really not that way, and in fact I would say it's the reverse.
~~~Larissa