> Is there any website which lists the organizations using IB/FB and
> the some other details like number of users etc?

I'm not aware of an official website, but Claudio has a list here:
http://www.cvalde.com/WhoUsesIB.htm

Claudio, if you see this, can you please change "Sage U.S. Holdings,
Inc." to "Best Software" (we had a company name change).

We're IB VARs and have deployed over 8000 seats of InterBase to our
users since 1997. We support other databases as well.
http://www.CarpeDiemETS.com

David R.