Steven Vaughhan-Nichols at eWeek shows that IE usage has shown a significant 1% drop from 95.73 on June 4, 2004 to 94.73 on July 6, 2004. These numbers are based on websites averaging 20-40 million hits per day. So they are statistically solid. However, one conjecture is that this is likely not a major switch trend but comprises a core Netscape group returning to the fold.
Meanwhile Mozilla will launch a final version of Firefox in mid September and then embark on an ambitious new features development program. At the same time, Microsofts IE developers in a public chat with users would not committ to doing anything about security or bringing IE up to standards or releasing a new version of IE by any specified date.
So you owe it to yourself (and organization) to follow Steven Vaughan-Nichols excellent How To: How to Replace Imternet Explorer. This gives a fairly thorough look at alternatives and then step by step details on how to replace IE including a careful analysis of what to choose as replacements from some pretty good choices.