Recently introduced were Health Savings Accounts. I am told we have  3
million signed up for them? What is the average income of the people
using these accounts? Who are they?

I'm one of the people using an HSA.  It is attached to a High
Deductible Health Plan (HDHP).  I love the plan for myself, it's truly
amazing for a fairly healthy young adult (I had $0 out of pocket
expenses for medical/dental last year and I have $1,000 saved up in
the account already)
.  
Unfortunately these plans were new in 2005 so there is probably no
valid statistic on participant incomes... partly because it's so new,
and also because I don't think the providers are allowed to collect
that data when issuing a group plan.

But from the people I've talked to, the participants of these plans
(due to the nature of the plans) are almost entirely young single
adults with slightly above average income for their age.