**Update** - Apple has released iOS 6.1.2 which apparently resolves this Exchange Calendar Issue (http://support.apple.com/kb/DL1639).
In case you haven’t read any blogs or forums about this issue I wanted to communication our KB article that discusses the problem. Basically we are seeing problems around devices that have been upgraded to iOS 6.1 causing transaction log growth, CPU usage, and Memory consumption problems on CAS & MBX servers.
If you notice excessive IIS log growth on the CAS server you should look for the text below which keeps looping continuously.
2013-02-06 23:41:59 192.168.137.11 POST /Microsoft-Server-ActiveSync/default.eas
443 firstname.lastname@example.org 192.168.137.246 Apple-iPad2C1/1002.141 200 0 0 187
2013-02-06 23:41:59 192.168.137.11 POST
443 email@example.com 192.168.137.246 Apple-iPad2C1/1002.141 200 00 140
Also if you have enabled EAS Mailbox logging you might see the text below (Status 4) in some meeting requests that suggest the problem is happening.
The workaround can include recreating the device partnership, custom throttling policy, ABQ policy, and possible other Load Balancer rules. Take a look are the link below which gives all the details and also different ways to collect logs.