If you've restored the SharePoint site using commands Site --> Administration --> Restore site and this site had special XSLT data views you may be in for a big surprise!
You can receive the following message:
Unable to display this Web Part. To troubleshoot the problem, open this Web page in a Windows SharePoint Services-compatible HTML editor such as Microsoft Office SharePoint Designer. If the problem persists, contact your Web server administrator.
Or in Slovene language
Spletnega gradnika ni mogoče prikazati. Če želite odpraviti težavo, odprite spletno stran v urejevalniku HTML, združljivim s storitvami Windows SharePoint Services, kot je program Microsoft Office SharePoint Designer. Če težave ne morete odpraviti, se obrnite na skrbnika spletnega strežnika.
The problem is that while restoring the site, SharePoint designer doesn't correct the GUIDs of lists being used. For example: You're having an XSLT data view of a list called Contacts. When restoring SharePoint designer creates the list with a new GUID, but it uses the old GUID (from where the backup was made) of the list. The solution is simple: Fix the GUIDs of lists used in dataviews:
1. Open the Manage content administration page of your site (http://server/site/_layouts/mcontent.aspx)
2. Copy the shortcut of the list being used in XSLT to clipboard
3. In the URL you'll find the new GUID of a list between brackets ( in http://server/site/_layouts/ListEdit.aspx?List={89D731E5-0538-4999-B4AF-D7A5D9EA781F} the GUID is 89D731E5-0538-4999-B4AF-D7A5D9EA781F
4. With SharePoint Designer open the page with XSLT data view and search for term ListID in the code.
5. Select the value of the ListID parameter. It should be the GUID of the list (either in ListID="....." or in the same tag, look for GUID-like numbers.
6. Prest CTRL+H for Search and Replace with the value still selected. It will automatically populate the "Find what" field with it. Now paste the copied URL with GUID in the "Replace with" field and remove all but the GUID. Make sure you have the "Find in Source Code" option checked.
7. Now just press the "Replace all" button and your XSLT data view will magically come to life :).
I hope that this bug will be fixed with next version of SharePoint Designer, or maybe can develop some kind of plugin for that procedure to speed up the process for all the pages. I know that with FrontPage this wasn't happening.