XSLT Data View Web Parts have been and still remain to be one of the most powerful web parts in SharePoint , some people call it “The Swiss Army Knife of SharePoint Web Parts” , the only problem that I can see with the Data View Web Part that once you add it to a web part page, the end users cannot further manipulate it, they have to come back to SPD Designer to modify it or directly edit the XSLT from the browser which is not an easy task (All data is retrieved as XML and manipulated using XSLT which is a very flexible way of transforming and presenting your data). Otherwise, the XSLT Data View Web Part is a wonderful web part, you can aggregate data from a variety of sources and present them in an awesome way.
In SharePoint 2007, we also had List View Web Part, which could be used to show a list content in a page but you cannot customize it that much in SPD 2007, you have to convert it to XSLT Data View Web part in order to customize or extend it.
In SPD 2010, there is a new web part called XSLT List View Web Part which is a combination of both :
XSLT List View Web Part = List View Web Part + XSLT Data View Web Part
You can customize it directly through SPD 2010 and once it’s added to a page, end users can still customize it using the browser by adding views and doing anything that was possible using List View Web Part.
Ah, by the way the Swiss Army Knife of SharePoint Web Parts still exists in SharePoint Designer 2010 with a much better designer surface using the new Ribbons interface 🙂