Well the concern with a chair, 1st and foremost, is the comfort and its ability to be adjusted by height and the backrest. Material used to cover the cushion (i think black is usually what it comes in. We gamers tend to eat and pong game, any other colour may not work in our favour). Material used for the cushion itself. Ease of setup, bulkiness/weight, mobility and PRICE. Biggest factor for that sort of investment is the price.
Never had the opportunity to use a gaming chair but i can give you my 2c about what I would look for feature wise outside of practicality and comfort from what i've seen online.
We're talking about a gaming chair here, so there are key features which will be the selling point for it.
* Sound - surround sound with built in speakers in around the head rest, preferably using optical surround over simulated - volume control preferably built into the arm rest of the chair for convenience.
* USB ports - for those PC users who use controls and fight sticks etc, it would be a great aid having not only extra usb ports available but place especially for good cable management. Strategically placed clips to hold cables around the frame of the chair for the usb devices would be a great feature as well. This inherently brings up the problem that Mez and Doomtack mentioned about cables and wires being rolled over and broken and being an eye sore. Still can't think of a way around that =/. Only thing i can think of is wireless all the way.. but then the chair might need a PSU and a will still have a cord running to it lol
* Interface for consoles. Off the bat when i think of gaming chair i immediately think about PC gamers since i know most console gamers to just sit on the floor or the couch. There should be compatibility with the consoles for both chat peripherals (voice and text) as well as sound and controls (ports for audio input/output and again the usb). Bluetooth in the case of the PS3 and perhaps an adapter like what the Sharkoon/Triton have for the 360. Even the ability to charge remotes and a holder specifically for that may be epic similar to what Mez mentioned about charging wireless mice.
That's about it for now. When i get more time i'll look at some more chairs and see what else they have/don't have.