I know a great deal about Data View Web Part and there are numerous solutions I posted here which were created with it (Blog archive | SharePoint Lists and Libraries, Outlook Style | KPIs), however Laura taught me something new:
- Yes, you can use Data View Web Part to pull data from subsites
- Yes, you can use Data View Web Part to aggregate data from more than one list
The benefit: This is very important for Windows SharePoint Services users since you do not have Content Query Web Part in WSS. By using DVWP you might be able to aggregate and present information in very interesting ways.
The problem: Although DVWP can aggregate data from subsites you would have to pre-configure all the sources. In case you add a new site you will need to ad it to your data sources. (I presume it might not perform very well when multiple sources are used).
Conclusion: No matter how hard you learn, when it comes to SharePoint, there is always something new to learn. Keep your eyes open!