Loop through folder names on a server directory
Performance

If you really want to squeeze out every ounce of performance, I recommend early binding the FileSystemObject and related classes. From the "What form of binding should I use" from this MSDN article:


  Early binding is the preferred method. It is the best performer
  because your application binds directly to the address of the function
  being called and there is no extra overhead in doing a run-time
  lookup. In terms of overall execution speed, it is at least twice as
  fast as late binding.


Beyond that, there's not much more you can do in the way of performance. Most of the time here is going to talking to the remote file system. You could remove the ability to cancel or not update the status bar, but it's my belief the UX would suffer too much. 

One thing you could do though is alter how often you update the status bar based on how many subfolders are found. Instead of having IterationsToUpdate be a constant, make it a variable and figure out a way to calculate how often the status bar should be updated using the SubFolder's Count property. Perhaps update at each 5%. 

    IterationsToUpdate = CInt(Subfolders.Count * 0.05)




Update:

I changed my mind. There is something more you can do to make the performance better. Several things actually, but I'll let you decide if the second one is really worth it or not.


Stop Re-dimensioning the array. You already know how big it should be, so Dim it once and only once.

Dim MyArr(1 To objFolder.Subfolders.Count, 1 To 2) As Variant


This removes a lot of overhead inside of the loop. When you ReDim Preserve, you're effectively making a copy of the array at each iteration. There's no reason to do this when you know how big the array should be up front.


2. You could unroll the loop. Be aware, that doing this will cause a maintenance headache, but it *could significantly speed up the loop through the subfolders. This works by setting multiple "positions" of your array during each iteration.

*I do mean could. There's no way of knowing if it will actually perform better or not until it is tried and benchmarked.

Unfortunately, you can't access items in the Folders collection by integral index, only by key, so unrolling the loop is not an option.



Misc


Why delete the entire range here? Are all of those rows always filled? Could there ever be more?


wsOutput.Rows("2:1048576").Delete



It would be better to find the last non-empty row. 
Why are you activating here? Smells like an unintended side effect to me. 


 wsOutput.Activate



Perhaps you meant to select the range for the user? If so, the correct way to do that is this. 

 wsOutput.Select

You don't need parenthesis here. 


MsgBox ("Done")



You're wasting at least a few cycles telling the runtime to evaluate the default property of... a literal. I recommend reading over this StackOverflow Q &amp; A that details the rules about using parenthesis in a routine call for more information. 

It would also be nice to display the "Information" icon on the message box. It's a nicer UX. 

 MsgBox "Done", vbInformation

Consider using another constant here instead of the literal 18. 


If Err.Number = 18 Then



It's pretty clear what's going on from the context, but if I want to know exactly what that error is, I'd have to look it up. A (well named) constant keeps the maintainer in the IDE as it removes any ambiguity.