I've developed a new version of the bookmarklet, which is now over here.
The new version uses the Bootstrap theme for a contemporary look and feel. It also has a useful textarea box so you can quickly copy and paste the on-page seo elements into another document.
2008 version below:
This version has been left in case of edge case comptability issues.
Drag this link to your bookmarks toolbar
Clicking on it will give you a quick overview of the on page attributes and produce an example of how the page will appear in the Google SERPs.
Given that data it's easy to tailor the page's title and description to create a more dynamic and clickable search engine result which should have a better click through rate than a keyword heavy title writen for the search engines and not for your audience.
I'd be grateful if you would please leave your comments and ideas on the SEO Bookmarklet page so I can continue to improve this tool.