Usually when I'm visiting my clients, I lug along a computer bag filled with various tools along with my MacBook Air. The rest of the time, I'm either in my office with my iMac, or away from a Mac enjoying myself. Unfortunately, Mac issues tend to arise at the worst possible times, and so there are many situations where I only have my iPhone available for support.
One of my tricks of the trade is to talk with clients while looking at their Mac screens using a remote support tool, and the iPhone screen has always been too small to be useful. When you're trying to control someone's computer through Jaadu VNC or some other remote control software, screen real estate is very helpful. I can see using the iPad for remote support in many situations where an iPhone just won't work.
The iPad would also be useful for reading technical documentation while on-site. I have many support documents saved in PDF format and saved into my Dropbox; they'll be much easier to read on the iPad screen than on my iPhone. Likewise, when I've tried to pull up support info from a number of websites with my iPhone, I've found reading the support articles to be nearly impossible.
With the built-in 802.11n Wi-Fi, the iPad is going to be useful as a very portable device for troubleshooting wireless networks. Apps such as the US$4.99 iNet Pro network scanner [iTunes Link] will work on iPad right off the bat, so they'll find a place on my iPad home screen.
Of course, there are some things you'll never be able to do with an iPad. For example, it's sometimes helpful to start up another Mac in Target Disk Mode and run a utility on a laptop to check for disk issues on the ailing Mac. Since the advent of the MacBook Air and new MacBook, some of the lower-end laptops don't even come with the requisite FireWire port to allow this type of connection. My solution was to use an old iPod loaded with TechTool Pro; there are ways to load Mac OS X onto USB drives as a boot drive as well.
Likewise, there's no way to run Windows-based applications on the iPad... yet. However, many remote control apps for iPhone are cross-platform and supporting Windows machines from the iPad would be possible.
If there are other Mac support consultants out there who are thinking about how to use the iPad in their businesses, please leave a comment telling us how you think the device could be utilized to help out your clients. I, for one, am looking forward to going on service calls with nothing but my iPhone and iPad.