"What % of US based Web Merchants use Quickbooks as their backend
accounting system?"

I have developed an e-commerce Tool for small to medium businesses who
sell merchandise on the Web.  This tool synchronizes orders data from
the merchant's website with inventory data in Quickbooks 2002,
Quickbooks 2003 and Quickbooks 2004 versions only. Quickbooks is the
leading accounting software for small businesses.

BACKGROUND: (i.e. what leads me to ask and formulate my question):
I have a mailing list of 150,000 US based web merchants, but the list
represents the GENERAL population of web merchants, not just small web
merchants, and definitely not what I really needed - which is small
web merchants who use one of the 3 Quickbooks versions as their
backend accounting software.  Since I am going to be doing a regular
mail campaign (not an email campaign), I want to make sure that this
mailing will be seen by enough Quickbooks users so that the campaign
is economically viable. That is why I need to know the specific answer
to my question.

What I don't need in an answer:  
I really don't need to know the OVERALL market share of Quickbooks,
market share growth trends, etc.  The answer must focus on the number
of US based web merchants and how many of them use those 3 versions of
Quickbooks, so that I can calculate exactly how many potential
customers are hidden in my mailing list of 150,000 US based web
merchants.

Hi cybershipper,

The following may provide you or other researchers a starting point
for your research:

"Quickbooks enables small organizations to automate many of their
accounting related functions, including bookkeeping, invoicing, and
billing, and is the market leader in its category, with a market share
in excess of 78% (based on recent NPD retail sales data). We estimate
the company had approximately 2.6 million Quickbooks users at the end
of April. According to the Small Business Administration,
approximately 600,000 new companies start each year in the United
States, and Intuit estimates that approximately 400,000 of them select
Quickbooks for their accounting needs. In our opinion, Intuit was able
to garner such a significant portion of the market for the same reason
its Quicken product did; it?s easy to use and lets ordinary people
without accounting degrees effectively and efficiently manage the
finances for their businesses."

RBC Capital Markets
https://www.rbccmresearch.com/drw1.0.4/pdf/0,,41068,00.pdf.
(Needs Adobe Acrobat)

Best wishes,
rainbow~

Thanks, rainbow-ga.  This is very helpful, and will be a good data
source for the researcher.  The real challenge is to find out how many
US based web merchants exist today, and how many of them use
Quickbooks.