There are several great improvements to the interface that allows you to add web parts to the page. When you choose to edit a SharePoint 2010 site you are given several different options in the Ribbon for the addition of web parts. The screenshot below shows the three options I am referring to:
What is great about this is that you are able to easily able to add new web parts, or create new lists if needed. If you know that the web part you want to add is an existing list you can click existing lists, otherwise you can select Web Part to see a list of all available web parts.
When you add an existing web part, the ribbon is expanded to show the web parts grouped by categories. This is a big improvement over have a long list that you have to scroll through to find the web part that you are looking for. For each category the web parts are displayed, along with a description of the web part.
If you notice that the list you need has not been created for the site yet, you can select the option to create a new list. When you create the new list, the new list web part is added immediately to the page, in the same way it would be if the list had already existed.
To me this is one of those small improvements that can potential save some time and frustration when creating sites. I know many times I have been working on a site and realize that the list / library that I want to reference doesn't exist on the site yet. This could definitely help reduce the steps required to get the site built.