AllowUnsafeUpdates RunWithElevatedPrivileges

What does AllowUnsafeUpdates do ?
If your code modifies Windows SharePoint Services data in some way, you may need to allow unsafe updates on the Web site, without requiring a security validation. You can do by setting the AllowUnsafeUpdates property.
Ex:
using(SPSite mySite = new SPSite("yourserver"))
{ using(SPWeb myWeb = mySite.OpenWeb())
{
myWeb.AllowUnsafeUpdates = true;
SPList interviewList = myWeb.Lists["listtoinsert"];
SPListItem newItem = interviewList.Items.Add();
newItem["interview"] = "interview";
newItem.Update();
}
}
What does RunWithElevatedPrivileges do?
Assume that you have a Web Part in which you want to display information obtained through the Windows SharePoint Services object model, such as the name of the current site collection owner, usage statistics, or auditing information. These are examples of calls into the object model that require site-administration privileges. Your Web Part experiences an access-denied error if it attempts to obtain this information when the current user is not a site administrator. The request is initiated by a nonprivileged user. you can still successfully make these calls into the object model by calling the RunWithElevatedPrivileges method provided by the SPSecurity class.
Ex:
SPSite siteColl = SPContext.Current.Site;
SPWeb site = SPContext.Current.Web;
SPSecurity.RunWithElevatedPrivileges(delegate()
{
using (SPSite ElevatedsiteColl = new SPSite(siteColl.ID))
{
using (SPWeb ElevatedSite = ElevatedsiteColl.OpenWeb(site.ID))
{
string SiteCollectionOwner = ElevatedsiteColl.Owner.Name;
string Visits = ElevatedsiteColl.Usage.Visits.ToString();
string RootAuditEntries = ElevatedSite.RootFolder.Audit.GetEntries().Count.ToString();
}
}
});