I use an iPad and a Blackberry Playbook at the moment for tablets, and an Android for a phone.
I don't know that I would really use an app on the tablets, and the pdf readers built in work fine for the books.
My issue is that I wish you guys would offer your .pdf's online for download already optimized for mobile. It can cut the size of the PDF's by two-thirds.
Under Acrobat X Pro, you just go to File -> Save As -> Optimized then choose "Mobile" from the dropdown box at the top. Make sure transparency is not checked in the box to the left, and let it run, everything else can be set to default.
5 minutes later you have an optimized PDF, perfect for tablet viewing.
We can't do this with the protected files we download from the paizo website, but it would be great if we could just download them that way (complete with DRM).