I never (intentionally) hide an app with ⌘H, which could be rebound for each app (e.g. Finder), but this is obviously the wrong approach. So, (how) can you disable ⌘H for application-hiding in one fell swoop?
You might use a private.xml like this with Karabiner (formerly KeyRemap4MacBook):
<?xml version="1.0"?> <root> <item> <name>test</name> <identifier>test</identifier> <autogen>__KeyToKey__ KeyCode::H, VK_COMMAND | ModifierFlag::NONE, KeyCode::VK_NONE</autogen> </item> </root>
In addition to the accepted answer, this can be accomplished easily with BetterTouchTool.
Open BTT Preferences. If it isn't selected already, select Gestures.
Under Select Application, select Global.
Add a New Shortcut: ⌘H and leave the Trigger set to No Action.
Close the Preferences window, and ⌘H should now be disabled for all applications.
The downside compared to the accepted answer is that this fix involves running an application. However since many Mac users are already running BTT in the background for other purposes, this fix can be done in a few seconds and might be simpler for some users.
If you do not want an approach for separate applications, but for TOTAL disabling of the shortcut, you can use Karabiner (FREE, and OPEN SOURCE :) ) and after installing it add a special complex modification rule
The link already contains the search query, so just look for
Prevent unintended command-h hide window and then click on
Import and you are done!