A plugin I've recently started maintaining currently checks to see if any bindings exist to its functions before creating the default ones. This makes it easy to setup custom bindings and not have to do anything about the default ones.

if !hasmapto('<Plug>MyFunction', 'n')
    nmap <buffer> <Leader>f <Plug>MyFunction
endif

What this doesn't do is keep these default bindings from clobbering existing mappings. How can I detect if, say, there is an existing normal mode mapping for <leader>f before clobbering it with the plugin's default mapping.