Not the management of hand-held systems, although that sounds like a good topic too (future post!), but more so management of your systems from hand-held computing devices.
Being the iPad advocate that I am, I'm going to focus this posting on the iOS platform.
Have I mentioned how much it annoys me (network engineer by trade) that Apple used iOS? Sigh.
So you're a network admin, you have an iOS device, and an IP network of servers, network gear, printers, and other appliances to manage. "Easy, pretty much everything has a web interface, I'll just browse to it, create a shortcut on my iPad, and BAM, I'm done."
I won't argue that is one way to do it, but I won't agree it's the best.
To start with, what is your management platform? Are you a shop running HP SiteScope management software? You're in luck - download the free SiteScope app for your iPad or iPhone. It's an iPhone app, so it'll work on the iPad, but doesn't take advantage of the bigger real estate afforded by the iPad (yet?). So there's your portable network/sys admin view into the current status of your systems.
Not a SiteScope user? Hmm, well there's other options...
Most ESMs (Enterprise Service Management Applications) have a web interface, you can shortcut that to the tablet; but likely the scale/layout will be designed for a PC screen, not a tablet so you will have to (if allowed that flexibility) create a custom dashboard for tablets.
So there's your high-level view into things, but when you really want to roll up your sleeves, here's some iPad apps I use and find practical:
IP Calculator - simple intuitive interface. Not for IPv6, but that's not a big problem for me (yet...)
VTrace - handy for troubleshooting routing situations in wide-area networks.
WinAdmin - RDP client to access those pesky Windows servers. Solid and reliable, easy to use. Even easier if you get a Bluetooth keyboard for your iPad.
MyRouters Pro - console management of multiple Cisco devices (you know, the real IOS?).
gUnit - being Canadian, I frequently have to make metric/imperial conversions; this tool is excellent at that.
Dropbox - my number one way to move files between my laptop & iPad.
Note Taker HD - have to take quick hand-written notes in a technical meeting, or sketch up network diagrams on the fly? This tool works fantastically for me (best with a stylus though).
I'm using all these apps on iOS 4.2.1 using the original iPad hardware.