I have used Fineprint (and its companion pdfFactory Pro) for several years, and can say that they are well worth their cost.
Let me reiterate a few key points about what makes Fineprint so great. Some of these have already been mentioned but I just want to restate them for clarity:
* It installs itself as a printer so you can choose to print directly to it or set it as the default printer. When a print job is sent to it, it pops up with a preview of the job, and at that point you can send it to any physical printer you want, including an extremely convenient checkbox to activate duplexing on-the-fly without having to go into the printer settings dialog.
* Of course the 2-up, 4-up etc features are great. I like the fact it has a bypass feature to not apply any formatting/margins/etc but you can still use the duplexing option and force different jobs to start on a new sheet (so they don't start on the back of a page for example)
* When you print something to it, and the preview pops up, YOU CAN STILL PRINT JOBS to it. This is VERY handy if you are browsing the web and want to 'collect' various printouts of things you see. For example, shopping for computer parts, getting recipes off the web, etc etc. This is probably the nicest thing about it in my opinion, and when I tried it out long ago this was the feature that totally sold me on it.
* Once the jobs are printed, you can go through the entire job and delete pages you don't want (or undelete them too).
* If you have pdfFactory Pro you can print directly to it from the job preview.
And to the individual who asked about printing page numbers in Fineprint (superboyac), you can easily do this by creating a stationary with the page number in the header or footer.