User agent sniffing is evil and should be avoided at all costs, and it seems even Microsoft has admitted that, of course only after encountering the problems themselves by preparing a new version of their browser after 7 years, but still, better late than never:
If you run a website please check you are not unnecessarily blocking access based on the browser and version being reported.And from an entry in the official MSIE7 weblog:
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.One of the most important web sites that Microsoft runs is fixed in regards of browser sniffing. I pointed out in an earlier weblog entry that MSDN served different content to Opera browsers, for no specific reasons. What's worse is that it gave it worse and broken content. There was even added an entry in browser.js (A bundled-with-Opera and auto-updated script that runs on websites and fixes them if they are broken) to fix the problem.
Luckily, now it seems that they have taken their own advice and they are not serving different content anymore. Well done, and welcome to the process of fixing the web. Hopefully this is just the the first step in starting to do things the right way