Almost exactly one year ago I started work redesigning a large, complex and very un-friendly joomla 1.0 web site.
The site had been built in a rush and had grown rapidly with thousands of pages and a very poor navigational structure.
Users were regularly complaining that they could not find important information even though we knew it was there.
As a source of information it faired badly and the general impression was that it was disorganised and unprofessional and not a good representation of the organisation.
Joomla is great but I bet everyone has their own set of extensions that they always install on a site, I know I do.
This will either mean that you have to spend extra time installing them before you can get started on the real work or that you have built your own custom joomla install.
I've built several of them myself in the past and they must have saved me tens of hours.
It's relatively easy to do it but is in itself time consuming and of course you have to ensure that you keep all of the constituent parts up to date.