I use my iPad all of the time. Of course, I have my calendar, email, and contacts synced to it. I use it to check my calendar any time that I am in court and the judge plans to schedule an upcoming event. But the most important and frequent use I make of it is to access my files, which live in the cloud. I can look at any client file at any time (except one time when I was in the basement of one of the State office buildings and had no cell reception). I no longer carry a paper file anywhere -- if I have papers that must be filed or delivered to someone, I will carry just those in a document sleeve. I have been able to make disclosure to opposing counsel before leaving his office during a deposition (he found that impressive).
Additionally, though, I use the iPad for marketing purposes. I check Twitter, Facebook, Google+, LinkedIn, and website statistics. I find the iPad is much more user-friendly for a status update on-the-go than my phone, which despite its giant screen still has a tiny onscreen keyboard. With the Google Voice app, I can check my voice mail, even while in court or a meeting. I have had clients digitally sign representation agreements on it, and it can work as a portable document scanner. Of course, on occasion I'll use it to play Sudoku, but just for a few minutes.
There are several versions of the iPad out there, and it can be daunting to choose among them. I would recommend the new iPad with Retina display, which has a larger screen and a newer processor. As for storage capacity, if you use cloud storage, this is less important, so you likely can get by with 32GB, or even 16GB. You must, however, get one with both Wi-Fi and cellular capability, so you can make use of it outside the office. When a Wi-Fi network is available, though, you should make use of it to save on your data plan. While I use and recommend Verizon, your existing cell network will likely work for you.
I'll admit, I was reluctant to get an iPad, and not sure that I'd be able to make much use of it in my practice. Now that I have one, I wonder if I would be able to run my practice without it. Please, check it out!
* Really, many of these functions can be accomplished with other tablet platforms, such as the Google Nexus or Microsoft's Surface. I really can't say how those platforms compare, though, not having used them. I can say that the Surface does not appear to have the same wireless connectivity options as the iPad, which would require offline syncing of client files. I also will say that the iPad is very user-friendly and widely supported. And while the Google Play Store is exploding with apps, many app developers only create an iPad/iPhone version of their product, whereas it seems that few make only an Android version.