I've had my Kindle for almost two years, and it is WONDERFUL. Everyone I know personally who has an e-reader owns a Kindle -- I don't personally know anyone who has a Nook. I've only talked to one person who's tried a Kindle and disliked it, and in her case it was a "book purist" thing.
Yes, you can get lots of free books, but you have to know how it works: If you go look right now, you'll get the idea that the free books are almost exclusively old classics that're out of copywrite (Dracula, Pride & Prejudice, etc.). If you keep looking week after week, you'll see that the truth is that those old classics are ALWAYS there for free . . . but the more modern stuff comes and goes. New authors put their things up for a couple days FOR FREE, and then they start to charge. Established authors often offer up some of their older stuff FOR FREE to get you thinking about them again. Authors often offer FOR FREE the first book in a series, hoping that you'll then pay for the rest of the series. They do this because LOADS of people "buy" their books for $0.00, which propels them into the Bestsellers category. Once they're in the Bestsellers, they gain visibility and they make money.
It'll be rare for you to find the exact bestseller that you want right now for free, but you're very likely to find something interesting, something that you didn't expect.
So the cornerstones of free books are as follows: Check Amazon.com often. When you see something that remotely interests you, get it. If you wait, it may cost money later. Finally, keep in mind that it's kind of like your favorite consignment store: Some days you'll find 8-10 great items. Other days you'll not find anything at all.
Having said that, I wouldn't get the Kindle JUST in hopes of lots of free books. I absolutely love mine, but if you get it for just this reason, I think you're going to be disappointed that you can't get the exact books that you want for free.