I have a Herman Miller Aeron with PostureFit. I used to sit on one of my wooden kitchen table chairs all the time and always had lower back pain. A good chair is expensive but well worth the cost.
At my office we have the Human Scale Freedom's which are also comfortable, but not as adjustable. We've had 2 break (1 arm rest, one handle on the back) recently, but other than that they are great chairs.
Was it worth the cost? Yeah, yeah it was.
Ignoring the ergonomic benefits, it's just a damn good chair. It's very comfortable. The tilt options are particularly good. I've been known to drag it into the living room to watch TV on if I'm having a bad posture day.
And the lifetime guarantee is really nice, and appears to Really Mean Lifetime. The seat started going about three months ago - I phoned HM up, and a new seat turned up in a truck about a week later.
I can imagine not buying another chair for 10-15 years or more, and at that sort of timescale, it's a bargain.
(See also: the Captain Vimes "Boots" theory.)