Fixed a couple threading issues. Improved the performance of the nodeSorter but this should be better improved in 6.x

src/umbraco.cms/businesslogic/CMSNode.cs

@@ -1,7 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Data;
-
+using System.Runtime.CompilerServices;
 using System.Xml;
 
 using umbraco.cms.businesslogic.web;
@@ -1036,6 +1036,12 @@ order by level,sortOrder";
 
         }
 
+        /// <summary>
+        /// This needs to be synchronized since we are doing multiple sql operations in one method
+        /// </summary>
+        /// <param name="x"></param>
+        /// <param name="versionId"></param>
+        [MethodImpl(MethodImplOptions.Synchronized)]
         protected void SavePreviewXml(XmlNode x, Guid versionId)
         {
             string sql = PreviewExists(versionId) ? "UPDATE cmsPreviewXml SET xml = @xml, timestamp = @timestamp WHERE nodeId=@nodeId AND versionId = @versionId"

src/umbraco.cms/businesslogic/web/Document.cs

@@ -1756,6 +1756,10 @@ where published = 1 And nodeId = @nodeId And trashed = 0", SqlHelper.CreateParam
             }
         }
 
+        /// <summary>
+        /// This is a specialized method which literally just makes sure that the sortOrder attribute of the xml
+        /// that is stored in the database is up to date.
+        /// </summary>
         public void refreshXmlSortOrder()
         {
             if (Published)
@@ -2002,6 +2006,11 @@ where published = 1 And nodeId = @nodeId And trashed = 0", SqlHelper.CreateParam
             return temp;
         }
 
+        /// <summary>
+        /// This needs to be synchronized since we're doing multiple sql operations in the single method
+        /// </summary>
+        /// <param name="x"></param>
+        [MethodImpl(MethodImplOptions.Synchronized)]
         private void saveXml(XmlNode x)
         {
             bool exists = (SqlHelper.ExecuteScalar<int>("SELECT COUNT(nodeId) FROM cmsContentXml WHERE nodeId=@nodeId",