Dropping IE6 and IE7 support
Internet Explorer 6 was released in 2001, Internet Explorer 7 in 2006, and this two are currently the most obsolete browser still used, and they gives many problems in the web development because of theirs numerous website visualization bugs.
The user base
We are in 2011 with the about 20% of users that still uses IE6 or IE7, because Microsoft still refuses to implement an automatic update, following irrational logics related to the sale of the Windows operating system, and then tying the users of the Windows operating system to a browser fated to become obsolete.
Actual browsers user shareAdditional work for support
This two browsers require a heavy additional work from the web developers to have a properly display of the website, and for supporting some css you can't even find a fix, so the designs should be studied appositely for IE6 and IE7, so that many designers and developers already have stopped to support IE6, and they refuse to develop for that old browser. Among these also giants like Google, Youtube and Facebook have decided to drop IE6.
“Google has good commercial reasons encourage IE6’s demise. Their future strategy and web applications depend on newer web technologies such as Html5, which do not work in older browsers.”sitepoint.com - Craig Buckler
Conclusions
Personally i decided to drop IE6 and IE7 support (also IE7 has many limitations), adopting however a precaution: I present to the visitors an alert that invites them to update the obsolete browser, thanks to IE6 no more.
The warning to update the browser of 'IE6 no more'To warn the users to upgrade the browser is a good contribution to the web, that see today the advent of css3 and html5; with a modern browser the users can appreciate the new functions and a much more reactive browsing experience, with a fast rendering and loading of the pages.