As mentioned in the, programmatically reading MAPI properties by using APIs such as Extended MAPI the PropertyAccessor object in the Microsoft Office Outlook 2007 object model is supported.
Here's how we do it in C++.

#pragma warning(disable:4146)

#import "C:\Windows\System32\stdole2.tlb" rename_namespace("Outlook")
#import "C:\Program Files\Common Files\Microsoft Shared\OFFICE12\mso.dll" rename_namespace("Outlook")
#import "C:\Program Files\Microsoft Office\OFFICE12\msoutl.olb" rename_namespace("Outlook")

#pragma warning(default:4146)

#include <stdio.h>
#include <tchar.h>

using namespace Outlook;

struct StartOle


void dump_com_error(_com_error &e)
    _tprintf(_T("Oops - hit an error!\n"));
    _tprintf(_T("\a\tCode = %08lx\n"), e.Error());
    _tprintf(_T("\a\tCode meaning = %s\n"), e.ErrorMessage());
    _bstr_t bstrSource(e.Source());
    _bstr_t bstrDescription(e.Description());
    _tprintf(_T("\a\tSource = %s\n"), (LPCTSTR) bstrSource);
    _tprintf(_T("\a\tDescription = %s\n"), (LPCTSTR) bstrDescription);

void main(int argc, char* argv[])
  _ApplicationPtr pApp("Outlook.Application");
  _NameSpacePtr pNameSpace;
  pNameSpace = pApp->GetNamespace(L"MAPI");

  MAPIFolderPtr pAppointmentMAPIFolder;
  pAppointmentMAPIFolder = pNameSpace->GetDefaultFolder(olFolderCalendar);

  _ItemsPtr pItems;
  _AppointmentItemPtr pAppointmentItem;

  pItems = pAppointmentMAPIFolder->GetItems();

  printf("No of items : %d\n", pItems->Count);

  pAppointmentItem = pItems->GetFirst();

  /* The following code uses GetPropertyAccessor: gets the user property WORKS */

  _PropertyAccessorPtr pPropAccPtr;
  pPropAccPtr = pAppointmentItem->GetPropertyAccessor();
  _variant_t var;
  var = pPropAccPtr->GetProperty(L"{00020329-0000-0000-c000-000000000046}/SomeID");

  /* The following code uses GetUserProperties: does not get the user property DOES NOT WORK */

  //UserPropertiesPtr pUP;
  //pUP = pAppointmentItem->GetUserProperties();
  //UserPropertyPtr uPP = pUP->Item(L"SomeID");
  //_variant_t var;
  //var = pPropAccPtr->GetProperty(L"{00020329-0000-0000-c000-000000000046}/SomeID");
  //var = uPP->GetValue();
 catch(_com_error &e)