I've had my iPad 2 since July of 2011. My first trip with it was to the Family Law Section's Summer Conference on Mackinac Island. It is a great travel device. I also use it regularly in my appellate practice to read and annotate trial transcripts and the rest of the trial court file (scanned to PDF, of course). I've tried several PDF annotation apps such as PDF iAnnotate, but lately have been using Notability for that purpose. Documents to Go Premium handles viewing and editing MS Office documents. I use SugarSync to transfer and sync my case documents from my PC to my iPad. It works very well and I've never found the 16 GB storage (mine is the cheapest iPad 2 model) to be a limitation. Lately I've been leaving paper behind when I fly up for appeal arguments and just sync the case file, including briefs, to the iPad.
But if you have more specialized needs, such as running Windows-only law office software, you can use remote access and control apps on an iPad or Android tablet to access your office (or home) PC and run your preferred Windows applications virtually. It's almost like being there.
The April 2011 Laptop Magazine had an post on iPad apps, most of which have an Android version, developed for remote access and control of your home or office Windows-based PC. The magazine reviewed three apps: GoToMyPC for iPad (no Android version), LogMeIn Ignition (both iPad and Android), and Splashtop Remote.
To the 3 reviewed by Laptop, I would add the remote app I have been employing with my Android phone for a couple of years, PhoneMyPC by Software for Me (no iPad version). For my wants, it has worked really nicely. I use LogMeIn Ignition on my iPad for this purpose, and clearly the iPad's larger screen provides a much more useful remote access and control experience trying the same thing on a phone.
If you are looking for resources for iPad apps for law practice, here are a few.