Sorry to bring this thread back from the dead, but I have a similar issue with my Kobo Touch.
I recently added roughly 900mb of books onto it, it has gotten to 45% on the "Processing Content" screen and has stopped there. The device will not respond to the power slide button, nor the reset switch on the back.
This was about 24 hours ago, and it is still in the same shape. Battery was fully charged when the transfer was started.
I have also sent an email to Kobo, hopefully someone can give me a positive answer.