Last year I installed an Ubuntu machine in one of the offices at work. It's still running well, but the evolution email client is not the best looking or most user friendly email client. Microsoft Outlook seems like a much superior product at the moment.
In an office environment the email client is one of the main programs people use to communicate, so having a good looking, user friendly email client is essential if we want to win people over.
What we need is a good looking email client that is highly compatible with exchange. Most companies use exchange, so it would be alot easier to add Ubuntu machines to the corporate network if those machines could handle email well.
The alternative is Thunderbird with better exchange/address book capability.