A <href=”http://marketshare.hitslink.com/browser-market-share.aspx?qprid=1”>Net Applications study</a> (via ReadWriteWeb) says IE’s market share has dropped to 67%:

This is an interesting trend. The actual quantity of market share will vary with methodology, but a 7% drop in a year is something to take note of. Moreover, as Readwrite points out, there are two things that will probably make the trend continue:

• The upcoming launch of mobile Firefox. I would also extend ReadWrite's point to cover the whole role of mobiles in general. The iphone's browsing share is now around 0.6%, a massive figure for a single phone. A popular phone to say the least, but one that still has a tiny share of the overall phone market. Just as basic mobiles are standard now across most of the planet, including developing countries, we'll be seeing a saturation of smartphones over the next few years. You can only say "but I just want to make phone calls" for as long as you don't see all the benefits others are deriving from all the other features. And we can be fairly certain that Firefox, Opera, and a whole range of niche browsers, many not yet born, will have the lion's share of browser action. Having struggled reluctantly with MS phones, I know personally the operating system is light years behind and mobile IE doesn't even have multiple tabs; it's not even in the race right now for anyone who has a choice.
• The trend towards cheap notebooks. Implicit here is RW's assumption that many will run Firefox on a custom Linux distro.

I was recently in a discussion with a developer who was considering an MS stack involving Silverlight on the client. His argument was about efficiency of development. I could debate that, but the greater point here is that we’ve gone beyond a time when it’s reasonable to go to market with an IE-only app. (I realise Silverlight is technically not just IE, but I am coming from a point of pragmatism here, and anecdotally you don’t want customers running Silverlight on other browsers and non-MS operating systems.). Even if it were more efficient to develop with MS tools, the constraint is too great.

In many organisations, people are exercising choice and using various browsers. Say you have 20 people in a company who are all potential users of your web app. What is the chance that all 20 will be using IE? Improbably low, assuming 67% chance that each is using IE. (Okay, somewhat of an exaggeration, because their usage will be correlated as they work in the same place, so it’s not 0.67^20; but still, gut feel is that at least a few people here will be running the Fox.) Even if the corporate standard is IE, I’ve never worked in a company that truly enforces their standard (thankfully for developers in particular), so I’d be willing to bet there will still be a number of folks running Firefox. By releasing a product that only runs on IE, you’re basically guaranteeing that it won’t run on all potential users’ browser of choice. Not a showstopper perhaps as they can still fire up IE - if you’re fortunate enough that they’re running MS - but still a great way to make your product unpopularly received. It might still be mandated if the decision is a central one involving a faceless someone or committee who could care less what browser it runs on; but it’s also possible that the decision-maker will be a Firefox, Safari, Opera, or Chrome user, and will be suitably unimpressed with a late ’90s style IE-only offering.