I am now the proud owner of a secondhand 1-year-old tablet.
I bought this Acer A500 from a colleague primarily for reading notes and e-books in preparation for the upcoming JLPT tests.
Once that's over though, this'd probably be mainly as a portable image browser. The built-in USB port means that connecting to keyboards, card readers, or even portable hard disk drives is a breeze. If combined with a Wi-Fi capable card such as the Eye-Fi, this could prove to be a very handy tool for on-site checking of details and immediate feedback.
Of course, nothing beats a full-fledged PC loaded with proper software when it comes to file management and editing. Even the cheapest of netbooks could easily outperform high-end tablets when it comes to sheer specs such as storage space and device compatibility. However, a tablet is usually more than sufficient for any task done away from the work desk.