On the principle of parsimony, the three symptoms reported are likely caused by a single bug.
1. 3G connectivity issues for all network users.
2. Repeated connects to MS Exchange.
3. Battery drain.
The one closest to the root cause being point 2.
Indeed this sounds like a regression. There was an old iOS bug previously fixed where for certain versions of exchange server, the mail client would get in an endless cycle of reconnects if the user switched on push notification. The connection would generate additional push notifications, which the mail client would try to process, generating more push notifications. When first encountered, very few users would have had their iPhones hooked up to exchange.
But if it has been re-introduced with a mass update now that the number if exchange users has ballooned, it's clear what the result will be. Huge simultaneous data usage on nodes where companies have many users in the vicinity accessing the versions of exchange where iOS mail has this problem - knocking out 3G for all users of the node and battery drain because of the continual reconnects. (for those who aren't familiar with software engineering, as counter intuitive as it may sound, regressions are a common occurrence, for certain classes of problem, if a bug is encountered and fixed once, it is far more likely to be encountered again in the future when further changes are made to code).
If it's a regression of that bug it was always debatable who's fault it was. But in my opinion MS win the argument on the principle that even if Exchange behaviour participates in the problem and is bad design wise, it is ok with MIcrosoft's own mail clients, and Exchange, released first, always exhibited the behaviour so Apple's clients, coming later, should have identified the problem and worked around it.