Pro Pack replaced the proprietary .rsr-format thumbnails with standard .png thumbnails, which are much easier to create in paint programs. Poser 5 added such features as multiple runtimes, subfolder support, a material library, and mouse-wheel support. It fixed the folder/file-limit bug, so your folder names won't become truncated as your library grows. It also tends to remember the last folder to which you browsed, rather than opening to the People folder by default. Poser 6 enhances the library further. You can now undock it from the side of the screen and move it elsewhere, resize the panel to view multiple columns at once, and save morph deltas directly to the library. Enhancements to the Material Room permit you to save all the materials on a figure now, instead of just one material at a time. In other words, the material files act more like MAT poses than before. I'm not that familiar with the current features of Pbooost, but after you move up to P6, you'll almost certainly have less need for it.