I may be missing something but why do people use Onyx anyways? It does stuff that OS X already takes care of.
I can verify and repair disk permissions with the Terminal/Disk Utility, I can manage my own browser history/caches/cookies etc, OS X runs the daily/weekly/monthly scripts on its own and if I really want I can remove the temporary items/system caches and whatever and I can rebuild Spotlight's index.
I really don't see the need to install Onyx. I don't know why people have been saying it makes OS X more fluid since clearing all the caches actually slows the system down as it needs to rebuild everything again. This certainly won't speed up the login time despite what one guy says. And maintenance apps might do more harm than good.
OS X is not Windows. It doesn't need maintenance. Don't worry about it and just use it.