Mountain Biking - Size For a 29er Hardtail

I'm 6 feet tall. I owned a 17" regular mountain bike and it seemed to fit me just fine, now I'm about to a buy a 29er bike (doesn't that make it even bigger?), and every single person I've talked to is still saying to get a 19". Is this necessary? Is it that big of a deal? Wouldn't I be absolutely fine on a 17" 29er at 6 feet tall?

Depends on the bike and how it fits you. I'm 6' also and my hardtail 9r is a 21, but I'm a roadie and like that stretched out aggressive position. Plus with lower back issues, more aggressive means more comfort for me. So I basically went for a setup that puts me in virtually the same riding position as when I'm on the hoods with my road bike. I'm sure it's not ideal for real technical courses where the size affects my turning ability, but who cares, I don't race and I'm comfortable riding it.

There's more to fit than just height. Your specific dimensions and the kind of riding you do can make quite a difference, not too mention the geometry of the bike. Without more info, it's hard to say what would fit you better. Can you try riding both sizes and see which fits better?

of course it depends on which bike. FWIW I ride a 17.5" 26er and a 17.5" 29er. a 17" frame sounds small for a guy who is 6' but if its comfortable it fits.

I'm 6' 300lbs 30" inseam, and ride a 19" Gary Fisher Rig. Fits me perfect. Top tube is a right at my balls but I have fallen and did not rack my balls at all. I will admit I was nervous at first but just felt cramped on a 17". FWIW I do have long gorilla arms so I probably feel more comfortable stretched out a bit.

Unless you're really weirdly proportioned, you'll probably feet a lot more comfortable on something bigger. Look into an 18" or a 19".