I use MacVim as my primary editor and since it uses hjkl as arrow keys and have gotten used to h and l representing left and right respectively. I prefer to use the keyboard over the trackpad (or mouse) wherever possible, so I wanted to replicate using these keys as closely as possible for working tabs.

MacVim has tabs, so what better than to start with that? In .vimrc, I map Ctrl-h and Ctrl-l to gT and gt respectively:

:map <c-h> <Esc>gT
:map <c-l> <Esc>gt

OS X allows you to configure and override keyboard shortcuts for menu items for any app. In System Preferences.app > Keyboard > Shortcuts. Under All Applications, I add shortcuts for Select Previous Tab, Previous Tab and Show Previous Tab, assigning them all to Ctrl-H. I add Ctrl-L for Show Next Tab, Next Tab and Select Next Tab. These shortcuts cover as least Safari, Chrome, Finder, HipChat, Terminal (and iTerm).

I also add app-specific shortcuts — Select Previous Conversation and Select Next Conversation for Messages.app, Previous Chat and Next Chat for Adium.app.

With this setup, I can use h-l as left and right when I’m editing a file in MacVim, use Ctrl-h and Ctrl-l to switch tabs both in MacVim and in most other OS X apps.