I have many sites with this old code which is intended to direct IE6 users to get a newer browser or to get Google Chrome Frame.
<!--[if lt IE 7]> You are using an outdated browser. Please <a href="http://browsehappy.com/">upgrade your browser</a> or <a href="http://www.google.com/chromeframe/?redirect=true">activate Google Chrome Frame</a> to improve your experience. <![endif]-->
The Chrome Frame link is no longer valid (it returns a 404).
Since this doesn't do anything for any significant number of visitors anymore, it doesn't seem to matter if I remove it or leave it. It may be best practice to remove it, but it would take time for each site.
The only downside I can think of to leaving this code unmodified is that perhaps it is a negative factor for SEO. Is it?