SharePoint 2010 SPSecurity.RunWithElevatedPrivileges HandleAccessDenied

The Microsoft.SharePoint.SPSecurity.RunWithElevatedPrivileges method enables you to supply a delegate that runs a subset of code in the context of an account with higher privileges than the current user.

Using SharePoint context with an unauthenticated user does not actually elevate privileges:

SPSecurity.RunWithElevatedPrivileges(delegate()
{
    // do something with SPContext.Current.Web 
    // fails with a HandleAccessDenied Exception
    // because SPContext is loaded with the site,
    // not within this delegate block.
});

So to get actual elevated privileges, you have to reload the context:

SPSecurity.RunWithElevatedPrivileges(delegate()
{
    using (SPSite site = new SPSite(this.Page.Request.Url.ToString()))
    {
        using (SPWeb thisWeb = site.OpenWeb())
        {
            // do something with thisWeb
        }
    }
});

See here for a better explanation: http://www.danlarson.com/spsecurity-runwithelevatedpriveleges/