How can I keep ~/Library visible in (Mountain) Lion
You can use Automator to create a simple app using the Run Shell Script action (with the chflags command within) and put it in your Login Items (in the Users &amp; Groups preferences). It will run every time you log in, so while OS updates will still re-hide the Library, you'll never notice.

Daniel Jalkut of Red Sweater Software has a pre-made app for this if you don't want to bother making your own. You can find it on his blog. Just download it and drag it to your Login Items.