An acquaintance of mine has recently undergone a merger at her corporation. As a mid-level employee, she knew it was coming; her company had announced a few months ago, but she hadn't heard any specific details other than it was going to happen.
When the time came for the companies to merge, there was confusion, misalignment, and miscommunication. Unfortunately when merging companies, often preparing employees for coming change has been left off the agenda or is an afterthought. Trust me that it is just as important, if not more so, to make the teams are prepared for the merger as it is to worry about day to day operations.