skim fullfills a differet role (adding notes and such). pdf cab just offers a quick way to open two documents in separate tabs so you can easily flip back and forth without taking up a lot of screen real estate.

Yeah and i gotta fix those icons..

Why not just use Skim (much much better for reading PDFs) and Shoka (freeware) or Yep (shareware)?

Hmm, looks useful but the UI could really use some work! Sup with dem icons?