Adobe have made the PDF format as difficult to work with for obvious reasons - they only want you to use their proprietary software to edit PDF documents.
Applications like PDFLab try to break this chain of control by allowing you to split and join PDF documents as well as insert images and blank pages. This is particularly useful if you're dealing with several PDF documents that you perhaps want to cherry pick pages from and then compile them into a new document. PDFLab is an extremely simple program - it only requires you to select the pages you want to extract from a document, put them in the order you'd like to see them and then create the new document.
More than this though, PDFLab even allows you to insert new images into a PDF page, encrypt or decrypt a document and add a watermark. Everything is easy to access via the menu bar across the top which categorizes each function namely Paper Size, Outlines, Postprocessing and List. Unfortunately, there seems to be little support and no forum offered by the developer in case of problems as sometimes, it either won't import some PDF files or inserting images won't work properly and there's no way of solving this. In addition, this app does not work on Snow Leopard yet after Apple removed Cocoa-Java components in the new OS.
PDFlab is however on the whole an excellent Swiss army knife for a whole host of PDF related tasks that don't very often come for free.
