First of all a HUGE THANKS to Yuval Sinay for putting this information together.
The following article will provide a summary on common issues in Exchange 2010 deployment in the Enterprise. The information in this article consists of my own experience and official Microsoft knowledgebase articles. Due to the fact that your Exchange environment may vary, please read the information carefully and test the suggestions from this article - in a lab that can demonstrate the current Exchange infrastructure.
The article is divided to the following chapters:
General issues in Exchange 2010 deployment.
Best practices in Exchange 2010 deployment.
Common issues in Exchange 2007 migration to Exchange 2010.
Common issues in Exchange 2003 migration to Exchange 2010.