Good points. In regards to CSS I think it's important to specify exactly what you mean though. I've seen this implemented dangerously where they simply position the form control off the wide (left:-4000px). This is vulnerable to browsers auto filling!

However hiding it completely with display:none should be safe and is what I think you mean.

In our case, just hiding it works fine. We can upgrade this to a CSS solution if we need to upgrade it though. The main point is if your doing something, you're ahead of the herd enough for spammers to generally leave you alone.