Visual upgrade: The visual upgrade feature in SharePoint Server 2010 is not available in SharePoint 2013
Document Workspace site template: The Document Workspace site template was removed from SharePoint 2013 to simplify the list of templates that are available when a user creates a new site collection. The Document Workspace site template will continue to operate in SharePoint 2013. The Document Workspace site template will be removed completely from the next major release of SharePoint and sites that were created by using the Document Workspace site template will not be supported.
Personalization Site site template: The Personalization Site site template was not a widely used site template. The Personalization Site site template was removed from SharePoint 2013 to simplify the list of templates that are available when a user creates a new site collection.
Meeting Workspace site templates: When you create a site in SharePoint 2013, all five of the Meeting Workspace site templates are not available. This includes the Basic Meeting Workspace, Blank Meeting Workspace, Decision Meeting Workspace, Social Meeting Workspace, and Multipage Meeting Workspace.
Group Work site template and Group Work solution: When you create a site in SharePoint 2013, the Group Work site template is not available. This Group Work site template provides a groupware solution that teams can use to create, organize, and share information. The Group Work site template includes the Group Calendar, Circulation, Phone-Call Memo, document library, and other basic lists. The Group Work site template and the Group Work solution are discontinued and not available in SharePoint 2013.
Unghosting and customizing CSS files: The following methods are included in SharePoint 2013, but will be removed from the next major release of SharePoint:
The methods are outdated and are no longer needed.
Excel Services — Can’t edit workbooks in the browser that have external data connections: This is a design limitation in SharePoint 2013.
Web Analytics in SharePoint Server 2010 Web Analytics in SharePoint Server 2010 has been discontinued and is not available in SharePoint 2013. Analytics processing for SharePoint 2013 is now a component of the Search service.
Search capabilities: The search capabilities of SharePoint Foundation 2013 have changed, and are now based on the same search implementation as SharePoint Server. This provides many improvements, but also means that the search configuration is very different.
Supported document formats: SharePoint 2013 no longer supports rarely used and older document formats that are supported in FAST Search Server 2010 for SharePoint by enabling the Advanced Filter Pack. Both the ULS logs and the crawl log indicate the items that were not crawled
Source : http://technet.microsoft.com/