The page doesn't work very well without Javascript. In my opinion/experience it's better to create a page in a fully usable form without javascript first. Then write a nicer/flashier/*er interface in non-intrusive javascript ( i.e. not inline javscript on elements but in a seperate .js file )
Don't forget to include a friendly reminder "This page has features that require javascript" for the paranoid freakjobs who have javascript off ).
I see that you're pulling in:
Prototype - from GoogleAPIs,
YUI - from YahooAPIs,
Tab.js - from Uservoice ( Who I've never heard of )
As a Tinfoil hat wearing NoScript user that's alot for me click allow on and seems very messy.
Surely all the functionality you use/need/want could be provided by Prototype OR YUI ( or my favourites Mootools or jQuery )
On the design front. Please, please, please get rid of those Image Headings that look like they're from cooltext.com in favour of a Text Header and a Text Link. The Black Border around the whole site probably isn't winning you any friends and the text layout needs some fixing.
For the section about installing the bookmarklet I would:
Put a heading on it like "Get Started Now!".
Change the tense of "Help me" to "Need help installing?".
use a border/background-color/different font to separate it better, although a heading could do this.
Align the top of it with the top of something else.