It's Take Your iPad to Work Day
Unless you use a Web-based mail tool like Gmail, device-specific mail apps are pretty well established and can be configured to manage multiple accounts such as personal and work e-mail. The same goes for calendar / schedule apps. Donor databases, however, are complex, and it is unlikely that sufficiently capable apps exist on all platforms. But all devices have Web browsers, so a browser-based database system is best as long as it can cope with being used in a variety of browsers and can scale from small screens to large. The only catch is you need to be connected to the Internet to use them.
Second, your donors
Whether they access your website from home or work, you no longer can make assumptions that it will be from a particular browser on a computer monitor. They probably BYOD as much as everyone else, so your website needs to work on all form-factors (or have a site that auto-senses the screen size and sends you to a mobile site when necessary), using all popular browsers.
Your interaction with them via social media should be catered for by the various platform-specific Facebook, Twitter, LinkedIn and YouTube apps. Responsive Web Design is a recent development that allows websites to adapt to the device screen on which they're being viewed. That means a single website would scale and display equally well on a smartphone or a large monitor - a trend worth keeping an eye on, as it means your donors would get the same Web experience whatever the device.
Third, your charity
The obvious benefit for organizations is that if the employees are buying these devices for themselves, the organization doesn't have to. It might also get more productivity from staff members, who are willing to check in during their own time.