The "late-September 2008 MobileMe update" support article is listed as being last modified October 29, but it's not clear when it was originally published.
The article says "Apple is always working to improve MobileMe. Since MobileMe is primarily a server-side, or 'cloud'-based, service, the MobileMe team can make improvements and push updates to MobileMe without any action being required of MobileMe customers. Since server-side updates are a bit more innocuous than a standard software update to Mac OS X or Microsoft Windows, it's easy not to notice that updates are occurring. Usually the only hint of these updates is that things just 'work better.'"
That suggests Apple would have brought the update to the attention of its users. Improvements cited in the report include improved localization for all of its web apps and better "membername suggestions when attempting to sign up for a membername that is already taken."
In the accounts section, the MobileMe update addresses accuracy of data transfer details, fixes an inaccuracy in reporting used storage on Group iDisks, improves the storage allocation menu on family pack sub accounts, and corrects account logout so that it properly logs the user out of the entire MobileMe session.
Under Mail, the update fixes a problem with performing a 'reply all,' fixes some keyboard shortcuts that weren't working properly within the browser, improves performance when using Internet Explorer 7, improves the performance of junk mail filtering and on initial login, fixes a problem with adding contacts within Mail, and it now displays a loading graphic as an email loads rather than just presenting a blank page.
Calendar has been updated for better performance with recurring events and with large numbers of To Do items, improved handling of international time zones, better performance on Firefox 3, fixes an event editor problem on certain browsers, and speeds up the initial loading of the Calendar.
Contacts now allows vCard export, improves IE7 performance, and fixes reliability when first loading Contacts.
Gallery has improved the ability to view Galleries on the iPhone and iPod touch, resolves a problem with buttons not displaying correctly on Firefox 3, and fixes the updating of photo information between the MobileMe website and published photos on the gallery.me.com site.
Additional updates to MobileMe are expected, including the advertised but still not yet delivered feature of uploading files from Mail to the service for download rather than as email attachments.