I think the Dream World is an awesome idea. Yes, it sucks on Firefox, yes, it's slow to connect, yes, you can't just choose which area to go to, but I think that adds to the challenge of setting out to find something, it's like Feebas in R/S, sorta, where you can't really know where it's going to appear, if it's going to appear, etc. :3
Just think though, guys, would you all be discussing Black and White now if the Dream World didn't exist? Probably not, because 1, global link poll, 2, new giveaways often, 3, new areas, and I really think it's kind of expanded Black and White in that it technically IS a sort of post-game. Sure the mini-games can be annoying, but if they wanted to make it easy to get the Pokemon then they'd just have made them all obtainable within the games with their hidden abilities and all. Oh yeah, and on that note, bet ya'll would be playing competitive Pokemon differently if a whole lot of Pokemon WEREN'T found in the Dream World (aka couldn't get their hidden abilities) and as a result the generation shift wouldn't have mattered. :x
Also, yes, it's annoying for those without wifi, but consider how many people have wifi these days compared to years ago for the western countries - it's kind of common now. And then there's the fact that Japan probably has wifi in every single home, making it work even better for Japanese players.
And I've probably repeated what a few others said (reading back, similar points), but I just really wanted to get this out. Dream World is definitely not a waste of time and can be really fun sometimes, too, so yes, I think it's a worthwhile feature. :)