Section 8.1 of the FAQ linked from php.net talks about 
using HTML forms to create arrays in PHP. It describes
the <input name="array[]"> syntax, but specifically 
mentions that you can't use array keys - which is wrong,
I'm not sure which version this was added in, but
you can happily do

<input name="array[key1]" ... >
<input name="array[key2]" ... > 

and use $array in your target script.

I find this terribly useful, so I thought it should be in 
the FAQ.