Web – Graded Browser Support
When developing web sites, how the site works and looks in different browsers should be tested. This can be a time consuming process of creating custom hacks, tweaking code, developing alternate workarounds or even ignoring incompatibility issues.
One of the main problems confronted is the selection of which browsers should be selected to test with. Yahoo developer network has created a list of "A-Grade Browsers". A-Grade Browsers are fully functional browsers which account for 96% market share.
http://developer.yahoo.com/yui/articles/gbs/
Testing time can be greatly reduced when used with browsershots.org
