SEO: Search Penalties from Hidden Text

Recently I was wondering why a website I created a couple of years ago is still only PR0, when I stumbled across an interview with Google's Matt Cutts. In the interview, Matt briefly mentions a search penalty for text hidden with CSS, specifically pointing out right: 999px.

Unfortunately I've been using a similar technique, text/image replacement:

h1 {text-indent: -9999px; width: 400px; height: 100px;
background: url(logo.png)}

The purpose of this is to replace the page heading with a logo. It seems highly likely the Google algorithm flags this as suspicious and issues a search penalty. I think it's time for a redesign! :-)