Due to the last change in the API of Twitter it is not possible to visualise the tweets in XML. As workaround you can use this search engine:
That allow you to query twitter for a particular set of tweets. For example if you want all the tweets of a particular user you can use the following syntax
The user is BiondiCarolibr
the XML site map plug in does not insert all the pages in the Sitemap.xml. In particular, in the case of online shops this result in the impossibility to add the product pages in the fine. Thus reducing the visibility of the products.
The best way to overcome this is to use the All in one SEO plugin in order to generate a second site map that should be inserted in google webmaster tools and bing.