Huge Library (60GB)!!!

Your root Library or your user Library? Your root Library will be, usually, about 3x the size as your user Library (my root Library folder, for example, is 35.23GB whereas my user Library is 11.44GB).

I tend not to mess around with either my root or user Library folders, so I'm not sure how to tell you how to go about trimming files therein. You might want to use something such as OmniDiskSweeper to see if there are any large (and unnecessary) files enclosed in those folders.

Clinton

You shouldn't use anything for what I call "periodic maintenance," running utilities to prevent problems that aren't ocurring.

Some third-party tools have useful routines to fix specific problems, but a shotgun approach, running all the tools in its arsenal, is never advisable.

OmniDiskSweeper just displays where all your storage is located in a graphical format.

My System/Library is only 6GB. Nothing should be growing in that folder. Nothing should be added to that folder by any programs.

"Maintenance" should only be done if your system is experiencing slowdowns, and does not need to be done on any regular schedule. The use of third-party utilities is fine, provided they are vetted to work with your version of OS X (some are, and some arent--Onyx is one of the more reputable ones though). Apple cannot guarantee their compatibility, so from their perspective you'll have to use these tools at your own risk, etc.

As for the large library, sometimes programs you install will keep massive databases of support files in folders like the "Application Support" directory, or at other times massive log files might be generated in the "Logs" directory.

Another option besides OmniDiskSweeper, is to use a graphical representation of file sizes in your specific folder, which can be done using a tool like GrandPerspective (displays relative file sized in a square grid), or DaisyDisk.

Having read your posts again, let's clear something up.

There are three Library directoryies.

The System Library is in /System/Library -- nothing should be adding to that directory

The "All User" Library is at the root of the hard drive /Library -- this is normally used for Library items that all users need access to.

The user Library is in your home folder, and is hidden in Mountain Lion -- user support files.

Which one is growing?