The iPad version of Shelf Life launched this morning. It provides a lot of the same functionality as the Mac version (All, Wanted, Reading List, and Finished tabs, as well as some of the Find functions and some reports).
If you have Shelf Life for the Mac, but would prefer it in the more portable form, you can import your Mac data files into the iPad version (you have to email them, then open the attachment on your Mail app on the iPad - the iPad will then prompt you to open the attachment in Shelf Life) - for full details, please see the included guide on the iPad version's Help tab.
Please note that the two versions do NOT sync with each other - however you can export from the iPad version using iTunes, and use that file on the Mac version - see the Help guide for further details.
Shelf Life for iPad is available from the App Store.