The ease of using Gmail for business was the main reason we switched to the service from other web based email. Training a new employee on gmail is unquestionably easier than training someone on many traditional email services.
The service is free for small businesses with under 10 people and very economical for every tier above that, that I've researched. There are also discounts for education, & non-profit organizations.
Many other services, beyond just Gmail, come with various packages. Basic membership comes with the Calendar and Drive. You have access to video chat, while some other services charge $5/user per month.
Room for Improvement:
Because it's all run by a single source, all of your services will be affected by google server outages. I have had more than a few outages here-or-there, which certainly affected my productivity, but these were resolved within an hour.
The free service comes with 25GB of storage, which is a lot for some, but certainly designers who E-mail large files might use up the space quickly.
Overall, gmail is the best form of email out there. I've noticed that most new employees either have their own personal gmail account and need almost no training, or become converts and quickly sign up for their own Gmail account shortly after using the service at work.