The short form of merlyn's answer is "use with impunity" =)

His point was that the "use Xxxx" happens during the "compile" stage, before the code begins to run. See use vs. require and use are helpful.

Oddly, the opposite topic came up just a week ago or so. Someone wanted to know HOW to make a "use" not happen at compile time. Here is one post from May Detecting modules in use? and the post from Oct 9, loading a module only if you need it.

Hope that helps...

--
$you = new YOU;
honk() if $you->love(perl)