For most activities involved in general pen testing a tablet or smartphone would be my last choice of platform. Yes, some folks have done full BT installs on them but that is more for amusement than anything else. Just not enough horsepower to do it directly from the mobile device. That being said, I use an ipad in the field to do some quick remote access into a server I use for pen testing. iSSH into the box to fire of nmap scans, msfcli, etc. That's cheating as the tablet isn't really doing any of the testing, just giving me quick access to the box that is. Some of the droid platforms can be used to do some wireless testing, but you're obviously going to be limited by antennas, injection capabilities, etc. You're also not going to be doing much WEP or WPA cracking on the mobile, but you might be able to pass it off to another system for the actual cracking. You can also find apps like droidsheep and others that are fun to play with, but still, more fun than functional.
CISSP, CISM, CISA, GCIH, GREM, CEH, HMFIC, KTHXBIROFLCOPTER