Apple updated a knowledge base article and noted that it basically rewrote MobileMe's underpinnings in a late September update.
The article, which carries an Oct. 29 date, outlines the following:
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".
AppleInsider notes this is a silent update, but if you follow the security side of the equation stealth updates and fixes are sort of the norm in the industry. Apple's QuickTime 
patches--rewrites--are epic. But across most software firms a lot of things get done quietly behind the scenes in updates.
In this specific update, Apple's list indicates to me that it basically called a do-over with MobileMe (all resources). For all services, Apple improved localization for MobileMe web applications and membername suggestions when attempting to sign up for a membername that is already taken.
For MobileMe Mail Apple fixed (Apple prefers "improved):
- An issue when attempting to Reply All to some messages
- Several issues with Keyboard Shortcuts not behaving as expected
- An issue in which a message was not removed from Drafts after being sent
- Performance in Internet Explorer 7
- Page title when you only have one message in a mailbox
- Performance when Junk Mail filtering is enabled
- An issue where attempting to add contacts from MobileMe mail was not working
- Performance when first logging into MobileMe Mail
- A "loading" graphic to indicate that messages are still being loaded instead of a blank page
For MobileMe Account Apple fixed:
- Accuracy of the MobileMe data transfer details
- An inaccuracy of used storage in a Group iDisk
- Storage allocation menu for family pack sub-accounts
- Logout from Account now fully logs you out of MobileMe
For MobileMe Calendar Apple fixed:
- Calendar performance with reoccurring events
- International time zone handling
- Performance in Mozilla Firefox 3 when switching views
- An issue in which event editors would only partially display in some browsers, requiring a refresh
- Performance with a large number of To Do items
- Reliability when first loading MobileMe Calendar
For MobileMe Contacts Apple fixed:
- The ability to export vCards from MobileMe contacts
- Performance with Internet Explorer 7
- Reliability when first loading MobileMe Contacts
And for MobileMe Gallery Apple fixed:
- The experience when viewing Galleries on an iPhone/iPod touch
- An issue where some buttons were not fully displaying in Firefox 3
- A photo's information in www.me.com/gallery will now correctly update the photo on gallery.me.com/membername
Clearly, MobileMe wasn't ready to launch (you don't fix this much after the fact). But since MobileMe has essentially launched its first service pack the big question is whether it works better. What are your experiences?
Also see: Apple’s MobileMe: Why don’t we just call it a beta