A survey conducted (see graphic above; click to enlarge) by email marketing software provider and consulting service ReachMail Media Services of over 1,000 respondents found that varying percentages of different worker generations attempted to adhere to "inbox zero," while other generations actually preferred using their inboxes as personal information managers.
Your next major concern will be compatibility. It's not a shock that most businesses run on Microsoft Windows and use some form of Microsoft Office. Being able to use common third-party clients such as Microsoft Outlook can often be a concern, and even today, compatibility with Microsoft Outlook isn't necessarily guaranteed. This is especially true when sending and receiving meeting invites. It only takes one garbled meeting invite to realize how frustrating this can be in the real world. Even if using Microsoft Outlook isn't a concern, portability is. If the service is entirely web-based, then is there a means for me to take my email offline and send email when I connect?