vbscript code:

wscript.echo now
For I = 1 To 3000
set ru=GetObject("WinMgmts:{impersonationLevel=impersonate}").InstancesOf("Win32_NetworkAdapterConfiguration")
set ru = nothing
Next
wscript.echo now

vbscript output:
C:\php\wmi>cscript wmi.vbs
Microsoft (R) Windows Script Host Version 5.6
Copyright (C) Microsoft Corporation 1996-2001. All rights reserved.
26/10/2002 00:07:26
26/10/2002 00:08:16

php code:

$prof = new Profiler;
for ($i=0;$i<3000;$i++){
$prof->startTimer($i);
$Services = new COM("winmgmts:{impersonationLevel=impersonate}") or die("glump");
$NetworkAdapterSet = $Services->InstancesOf('Win32_NetworkAdapterConfiguration');
$NetworkAdapterSet->release();
$Services->release();
unset($Services);
unset($NetworkAdapterSet);
$prof->stopTimer($i);
}

php results: 
C:\php\snaps\php4-win32-latest>php c:\php\wmi\wmiperf.php

Warning: (null)(): Invoke() failed: Exception occurred.
 <b>Source</b>: SWbemServices <b>Description</b>: Generic failure
 in c:\php\wmi\wmiperf.php on line 7

Fatal error: Call to a member function on a non-object in c:\php\wmi\wmiperf.php
 on line 8

doing it as 3 seperate runs yielded:
0-1000 runs: 11313.1239 ms (100.00 %) OVERALL TIME
1000-2000 runs: 23879.2120 ms (100.00 %) OVERALL TIME
2000-3000: 544210.0750 ms (100.00 %) OVERALL TIME

At the same time, memory utilization of winmgmt.exe rises to ~30mb from the normal 4mb...

Looks like something isn't getting freed right...