One of the purposes of releasing the IE7 beta is to collect feedback on compatibility with both websites and extensions and we continue to look at all the reports we receive of sites and applications not working. There are reasons for this such as the base tag change that we blogged about recently and also bugs that we are detecting that you’ll see addressed later in the project cycle. However the most common issue we continue to see for web sites not working are that they are blocking access or serving the wrong content as a result of the new User Agent string for IE7. I’ve seen some websites that when visited using IE7 ask the user to upgrade to the latest version of Internet Explorer or Netscape and other websites that serve content with very small fonts. Sometimes even some Microsoft’s own websites have been blocking access! A user can work around an incompatible website by adjusting the User-Agent string as described in a previous blog post. We now also have some additional documentation on MSDN to help:
I want to be clear that we do not advocate blocking access to content based on the User Agent string of the browser, as this practice results in users of unknown and newer versions of browsers being locked out. Rather than blocking unknown user-agents, consider using user-agent sniffing only in isolated cases to work around known limitations of specific user-agents.