Imposition software is definately the best way to go. Copy & Paste can throw up all sorts of problems: P20 mentioned H&Js, but if you lock to the baseline grid, or use complex text box linking, these can also cause problems.
Nowadays, however, you should be able to get your printer's pre-press guys to do it for you. In the last three printers I worked for, we all had imposition software which came with our RIPs. In fact, we PREFERRED people not to do their own impositioning because it usually created more work for us! So before you buy anything, check with your printer. Quark is expensive enough!