Via Jaap Vossers: Jaap has pulled it off again. Just recently he created yet another solution which enriches the standard SharePoint UI: introducing the SharePoint QuickLaunchExtender.
SharePoint QuickLaunchExtender extends the standard capabilities of the Quick Launch menu with a couple of new features. First of all you can expand/collapse the different sections. This resembles the Accordion Left Nav Feature by Paul Grenier.
Then you can expand the different sections accordion style:
Last but not least you Jaap has provided a third option to add a filter-as-you-type filter which allows you to filter the Quick Launch menu options as you type.
I think QuickLaunchExtender does some great job helping you declutter your UI. Especially when there are many things you would like to present to your users using the Quick Launch menu, SharePoint QuickLaunchExtender might be just the thing you were looking for to keep it manageable.
SharePoint QuickLaunchExtender is a great Feature: no doubt it. What I really like about it is that there is an Application Page which allows you to configure how you want your Quick Launch menu to look like.