I have used Aeron, an ergonomic chair for about 6 months, and I am a happy consumer.
See how Aeron adapts seamlessly to my messy environment below.

aeron

In his article, Hanselman stated that having a good chair is one of the most important thing. Jeff Atwood also said the same thing.
As a programmer, I normally spend hours in front of PC, whether it is for office work, personal work, or enterainment purpose.
I also don't want to have a back pain issue which is apparently a common thing for programmers.
Obviously, one of the reason I bought new chair is because my old $80 chair is already in bad state. It had served me for 5 years and its cushion is not good anymore.

Before buying new chair, my mind was already set to Aeron.
Aeron is an ergonomic chair from Herman Miller, and it is arguably the most popular office chair. It has good reviews and its hype got me. Having Aeron definitely makes me proud.
I did try to find other alternatives though.
My colleague recommended Ergohuman for me, which is also cheaper and already has headrest. The problem that I can't find any dealers in Indonesia.
People also has been saying that Herman Miller Embody and Steelcase Leap are the best right now. I asked Steelcase Leap dealer, and the price is more steep. Personally I also prefer mesh to cushion, that makes Aeron better in my opinion.

In Indonesia, Aeron is sold by PT Forum Indonesia, which is located at Jakarta.
The price was $1000 (+ $100 for 10% VAT), so it is definitely expensive, 13x of my previous chair's price !!! Fortunately it comes with 12 year warranty.

Aeron uses high quality mesh for its back and seating. At least, that's what I believe. It feels cool and I can sense air movement. It is also not hard on my back and butt.

aeron-back

Like common office chair, you can adjust its seating height and base arm.
However as an ergonomic chair, you can also adjust its tilt tension, which defines how far you can recline.
My mine also has PostureFit support. It gives pressure to my lower spine, so it tries to force me sitting in ideal position.

One thing to note is that it is important to have a correct size chair. I use its biggest size, C, which fits well with my back.
I can see that my Aeron won't be comfortable for persons with smaller body. Fortunately, Herman Miller has size reference for Aeron,

If you want a chair with headrest, unfortunately Aeron is not an option. Herman Miller's line of ergonomic chairs are not designed with headrest, and it is not recommended to buy third party headrest for Aeron.
There are a lot of mid to high end chairs with headrest, like Ergohuman, Humanscale Freedom or Steelcase Leap.
Personally I don't have any problem with headrest, as Aeron itself is a high back chair.

Is it worth buying ?
YES
Aeron is a popular ergonomic chair. Its design has a spot in the Museum of Modern Art's permanent collection !!
Aeron is comfortable and it has a lot of adjustable options.
Expensive, not designed with headrest