I think your stats are typical, although the numbers
vary widely depending on country and website. There's
an interesting article here:
http://blog.wired.com/monkeybites/2008/01/firefox-made-wo.html
Excerpt:
"XiTi Monitor reports a worldwide browser share of 66.1% for Internet
Explorer and 28% for Firefox (a new high). Opera has a 3.3% share and Safari
blips in at 2%. Also of note is the fact that over 90% of Firefox users are
running Firefox 2, while less than half of IE users have switched from IE6
to IE7."
So worldwide IE7 is about 1/3. Probably less in the US.
Certainly less in Eurpope. But IE7 is still a "boutique
browser". It will only run on XP (SP2?) and Vista. And
since it has "quirks mode", it's questionable how many
people are *really* using IE7 when it comes to rendering.
Your site is only rendered with IE7 changes if you use a
specific DOCTYPE tag.
If you want to install and test for IE7 because you're
designing to accomodate IE7 "standards mode", along
with older IE versions, that's up to you. I don't see any
point. It's bad enough that IE needs a different page
from all other browsers. With the limits on where IE7
will install I put it into the same categoryas Safari and
Konqueror: It's up to them to make it work. I'm not
going to test specifically.