Just over a week ago, I listened to Joel Spolsky and Jeff Atwood talking about chairs in their weekly stackoverflow podcast. Just yesterday, my manager did a sweep of our office asking if people are happy with their chairs, because one person had asked for a new one. My existing chair was actually broken so I asked for a replacement.
I previously read articles by both Jeff and Joel about equipping developers with a fancy chair and while I don't think they're wrong, having considered it, I still don't think I fit into that category. If I get uncomfortable at work, it's because I just spent 40 minutes playing football in my lunch break, don't want any more time to slip, so I skip getting a shower. Or I feel uncomfortable because we don't have air conditioning.
That said, even if I did decide I wanted a fancy chair, I doubt my company would see fit to buy me an aeron. Maybe if I'd been spoilt at some point, I'd come to realise the value of a quality chair, for now I'll just settle with the one my colleague is unhappy with.