I am not familiar with how Running Records are used to assess student reading but understand it is a widely used technique to assess a students reading performance. I have come across an app called Record of Reading which allows teachers to keep their running records on the iPad and then email the document as a PDF or JPG for filing. As I have mentioned I am not familiar with how these records are recorded so I can only recommend that if you want to use your iPad to do running records that you check out this app. I have added some blog posts from teachers who recommend its use if you are interested.
Reading assessment on the iPad (Australian)
Record of Reading App: Love this! (Australian)
Running records on the iPads (American)
Click here to visit the iTunes store to view the Record of Reading.