Google is a company that always aims to the future, and this reflects in how we treat versions of their software. For example, if you're using one of their services is probably the last version, because when a new version is launched, Google does best so that you upgrade.
Although you can not force other companies to follow the same spirit, she can no longer support older versions of software from other companies. And that is exactly what is happening with Google Apps.
The point is that Google wants to continue to develop new tools for your web services using the latest features, but at the same time, older browsers end up messing the update process.
Update difinitiva be in August
With that in mind, as of August you will not be able to rely 100% on any Google Apps service, as it will no longer work correctly in Internet Explorer 7, Firefox 3.5 or Safari 3.
Google has made this decision so that you are obliged to update them. If you do not, Gmail, Google Calendar, Google Docs, Google Talk and Google Sites are simply inaccessible.
The upgrade will cost nothing, it offers more features, more security, and probably a faster browsing experience. There is no disadvantage to get the latest browser on your machine.